Aphids Affecting Cannabis

Aphids are true insects within the order Hemiptera. Aphids are a relatively small group of insects, yet they are of serious economic concern in a variety of crops. About 25% of known crop species are affected by aphids. About 100 species are of serious economic importance [2]. They have a worldwide distribution, but are most commonly found in temperate regions. They can travel large distances passively on strong winds.

Most adult aphids do not develop wings, but a some do [3]. They feed on plants by utilizing a needle-like organ called a stylet. This allows them to bypass the plant cuticle and cells that contain defensive compounds.

Aphids are phloem-feeding, piercing, sucking pests that present a threat to crops through at least 4 mechanisms:

  1. Feeding damage- diverts nutrients intended for plant growth and reproduction to the aphids, causes physical plant damage which can lead to lower photosynthetic rates, increased transpiration, and lesions that can lead to pathogen infections.
  2. The injection of phytotoxins in to the plant during aphid feeding which can damage plant health and growth.
  3. Aphids are the most common vector of plant viruses. Nearly 50% of plant viruses can be transmitted by aphids [2], including viruses confirmed in Cannabis such as Cucumber Mosaic Virus (CMV) and Alfalfa Mosaic Virus (AMV) [3].
  4. Honeydew left on foliage by aphids can support the growth of sooty mold on leaf surfaces, leading to negatively impacted photosynthetic rates.

Cannabis produces the terpene β– farnesene, which acts as an alarm pheromone in the aphids [3].

What Aphid Species Affect Cannabis?

At least six species have been reported to infest Cannabis plants [3]. However, more recent information has challenged previous claims about which species colonize Cannabis. In Colorado, M. persicae and P. humuli were unable to survive on hemp plants after manual inoculation. It may be that previous reports of M. persicae and P. humuli as pests of Cannabis were actually misidentification of the Cannabis aphid, P. cannabis. Aphis fabae has only been reported once in the literature, and it may be possible that these other species may be misidentified or uncommon pests [14]. Given this information, IPM choices should generally focus on controlling P. cannabis, not other aphid species.

Myzus persicae (Green peach aphid)

A green (sometimes yellowish or even pink) aphid that is fairly large (about 2.0-3.4 mm long). The nymphs of the winged adults (alatae forms) are usually pink or red, while the adults have black-brown heads and a black spot on their abdomen.

In general, aphids are heteroecious, meaning that they migrate between two different hosts. M. persicae overwinters on Prunus species such as cherry or peach trees as eggs laid on limbs or tree bud axils. When eggs hatch, they give birth to fundatrices (stem mothers). These fundatrices can reproduce parthenogenically (asexually); they give live birth to 60-100 wingless clonal larvae called fundatrigeniae. The fundatrigaeniae give birth to more wingless females asexually (apterae or apterous viviparae). This continues until spring, when the first winged (alatae) aphids develop. These alatae females fly to alternate hosts such as Cannabis and produce more apterae offspring. Each aptera gives birth to 30-70 offspring until food becomes restricted, at which point new alatae (summer migrants) are produced to find new Cannabis plants. To reach maturity, each aptera offpring goes through about four molts on Cannabis. At the end of the summer, the aphids return to the primary host by special alatae called sexuparae. Upon return to Prunus hosts, the sexuparae give birth to ten sexuales.

In controlled indoor or greenhouse environments, M. persicae can replicate all year long parthenogenically on Cannabis.

can be male/female or alatous/apterous. When sexuales mate, females lay 5-10 eggs which overwinter on Prunus species. Using this life cycle, they are able to asexually amplify their populations on primary and secondary hosts.

Female adult green peach aphids, Myzus persicae (Sulzer), with immatures.
Image From http://entnemdept.ufl.edu/creatures/veg/aphid/green_peach_aphid.htm

Black Bean AphidAphis fabae

Overwintering host- Euonymus or Virburnum species.They represent at least 4 subspecies, and which subspecies which attacks Cannabis is unknown. Like M. persicae, eggs hatch in to fundatrices, followed by fundatrigeniae, then apterae. The rest of the life cycle is similar to M. persicae, and in the spring, winged females may infest Cannabis plants, which then produce more aphids asexually. They are found in all temperate regions except Australia, they infect many crops, and may vector over 30 viruses.

Aphids May 2010-3.jpg
Image from https://en.wikipedia.org/wiki/Black_bean_aphid

Bhang Aphid/Hemp Louse- Phorodon cannabis

These aphids are about 25% smaller than M. persicae (1.9-2.7 mm long). Their color can vary from colorless to bright green with dark green stripes. Alatae (winged) larvae are smaller than apterae larvae and have dark patches on the head and abdomen. Unlike M. persicae, P. cannabis does not alternate hosts (autoecious), and so sexuparae lay eggs directly on Cannabis, particularly on flowering tops. It has evolved to complete its entire life cycle on Cannabis plants.

As previously mentioned, P. cannabis is most damaging to Cannabis flowers; it prefers to feed on flower sepals and in seeded Cannabis, and shelter in between seeds and sepals. The bhang aphid has been reported as a common vector of Cannabis viruses including the hemp streak virus, hemp mosaic virus, cucumber mosaic virus, alfalfa mosaic virus, hemp mottle virus, and hemp leaf chlorosis virus. P. cannabis may have evolved from P. humuli, because it is autoecious but is indistinguishable from P. humuli aside from the smaller head of P. humuli and fewer bristles.

Image from https://influentialpoints.com/Gallery/Phorodon_cannabis_hemp_aphid.htm
Image from https://influentialpoints.com/Gallery/Phorodon_cannabis_hemp_aphid.htm

P. humuli

Much like M. persicae, P. humuli is heteroecious and overwinters on Prunus species. In the CA bay and southern England, spring migration of P. humuli alatae females to Cannabis happens in early and late June, respectively. Females can travel up to 150 km by wind. P. humuli normally infests hops, but can also infest Cannabis [3].

Phorodon humuli
Image from https://bugguide.net/node/view/637027

Melon aphid (A. gossypii)

First noted on marijuana in India, they are fairly small at 1-2 mm long. Color may vary from light yellow to dark green. The species has a broad host range but prefers warmer temperatures around 27°C and is a common vector of plant viruses.

Nymphs (mixed ages) and dark form of wingless adult of melon aphids, Aphis gossypii Glover.
Image from http://entnemdept.ufl.edu/creatures/veg/aphid/melon_aphid.htm

Abstrusomyzus phloxae

An aphid with a fairly large host range that has been reported in California in 2018 [31]. There is little information on this aphid, but it appears to be primarily asexual, with females producing parthenogenetically [32]. I am unsure how aggressive of pests they are, but they have been reported from both indoor and outdoor grows.

Image from https://aphidtrek.org/?page_id=32

Light green aphids- Consider M. persicae, P. humuli, and P. cannabis, though M. persicae is the largest of these species.

Dark green to black aphids- Points towards A. fabae or A. gossypii.

Distinguishing features between aphid species are usually based on the insect size, color/length of tubercles and cornicles or the size/presence of a midline knob. For instance, P. humuli and P. cannabis are smaller than M. persicae.

Signs and Symptoms of Aphid Infestation

Like mites, aphids tend to concenctrate on the undersides of leaves. Some species prefer lower leaves, such as Myzus persicae, and some species tend to feed on upper leaves Aphis fabae [3]. Some species of aphids even feed on the buds themselves, such as Phorodon humuli and P. cannabis, though they also feed on leaves.

Early symptoms are hard to detect, because they tend to be light colored spots on the bottoms of leaves near veins. It is important to check all parts of the foliage when you scout. As infestations progess, you will begin to notice distortions and strange growth patterns on developing foliage or flowers. Very severe infestations can result in plant wilt and even death.

Image from https://www.leafly.com/news/science-tech/the-curious-case-of-the-cannabis-aphid

Honeydew is another symptom of aphid infestation. It can sometimes be seen as shiny spots on the leaves, but it tends to not be very apparent on Cannabis leaves.

Aphid producing honeydew

Symptoms such as wilting or yellowing can sometimes be confused with symptoms caused by mites or whitelfies. Aphids have long wings at least twice the span of their body length, winged insects such as fungus gnats have shorter wings.


There is not a lot of information on control of the Cannabis aphid, as it is a fairly new pest in North America. Most recommendations will be based on control methods demonstrated to be effective on other aphid systems.

For indoor grows, sanitation and pest exclusion are very important. All air intake should be filtered or screened to exclude alatus (winged) females. Those entering the grow space should wash and not wear any clothing worn outside.

Genetic resistance introduced through selective breeding is a likely source of future control techniques, but right now there is not much knowledge as to which cultivars may be more resistant than others to aphid infestation.

Biological Control

Microbial Products

Bacillus thuringiensis-based products may have minor efficacy against some aphid species, but generally speaking is not a good choice for controlling aphids or piercing-sucking pests in general.

Monterey LG6332 Bacillus Thuringiensis (B.t.) Worm & Caterpillar Killer Insecticide/Pesticide Treatment Concentrate, 16 oz

Safer Brand 5163 Caterpillar Killer II Concentrate, 16 oz

Grandevo CG- Chromobacterium subtsugae

This product contains heat-killed bacteria as well as secreted metabolites. It works through various mechanisms of action

C. subtsugae is part of a recommended control program of the hop aphid (Phorodon humuli) along with B. bassiana and azadirachtin. Based on this, it has also been suggested as a control method for the very closely related Cannabis aphid (P. cannabis) [5].

Marrone Bio Innovations Grandevo WDG Bioinsecticide Miticide OMRI Listed – 6 lbs – 2019 Reformulated

Venerate CG- Burkholderia spp. strain A396

Like Grandevo, Venerate consists of heat-killed bacteria and secreted metabolites. Venerate is quite effective against M. persicae and is comparable with spirotetramat. It is more effective than C. subtsugae (i.e. Grandevo) for the green peach aphid [4]. For more broad control of various aphid species and other insect pests, it is recommended to rotate Venerate and Grandevo on a 7 day cycle.

Venerate CG Bioinsecticide Insecticide for Mites, Thrips, aphids, borers, whitefly, leafhoppers on Grapes, Strawberries, Potatoes, Citrus and More (1, Quart)

Marrone Bio Innovations Venerate CG Gallon

Beauveria bassiana

B. bassiana metabolites may have insecticidal activity towards aphids even without viable cells. B. bassiana culture filtrate (no living cells) is effective at controlling M. persicae [6], and even endophytic B. bassiana may negatively impact aphid populations on the colonized host plant [7]. B. bassiana has been shown to be effective against other aphids such as Macrosiphum rosae (the rose aphid), and Aphis gossypii (melon aphid) [8, 9]. It may also be effective against the cannabis aphid, as it has been demonstrated to be effective against the closely related hop aphid (Phorodon humuli) [10]. It is important that relative humidity is fairly high for B. bassiana to be effective. Ambient humidity levels should be at least 50% and the humidity at leaf surface would preferably be close to 80%.

BotaniGard 22WP Biological Insecticide 1lb

Isaria fumosorosea

Like B. bassiana, I. fumosorosea consists of live fungal spores and can spread throughout an insect population as the fungus sporulates on deceased insects. It has been demonstrated to be effective against some aphid species such as the brown citrus aphid [11], M. persicae [12]. It has limited effects on beneficial insects or predators and can be used along with other microbial insecticides. I. fumosorosea effectiveness may be decreased by the use of horticultural oils [13].

Purchase product PFR-97 from Certis USA, not available on Amazon.

Aphid Predators and Parasitoids

Green Lacewing (Chrysoperla carnea)

This larvae of this species are effective at keeping aphid populations low and preventing outbreaks without chemical control. Only the larvae are predatory. Adults lay eggs proximal to aphid colonies. They are also effective control for other common pests such as whiteflies. They tend to be most effective in enclosed locations with environmental control (indoor and greenhouses). They can tolerate warm temperatures, but do not operate well in cold environments. The ideal temperature and RH level is 20 ° C to 31 ° C and 70% respectively. Maintenance release rates are usually around 1,000-2,000 eggs/acre and infestation response can be up to 10,000 eggs/acre.

Green Lacewing Life Cycle
Image from https://biocontrol.entomology.cornell.edu/predators/Chrysoperla.php

Nature’s Good Guys Green Lacewing 1,000 Eggs – Slow Release Hanging Bag

Green Lacewing 5,000 Eggs – Organic Natural Aphid Control

Green Lacewing 10,000 Eggs – Organic Natural Aphid Control

Lady Bugs/Beeltes

I do not generally recommend ladybug releases for aphid control in Cannabis as a control method, unless in an enclosed environment with very high release rates. There needs to be a high population of aphids to keep them alive, and may require over 1,000 lady bugs per plant to actually get the issue under control. However, they can potentially work when released in high numbers in proper environments. For populations to persist, they may need to be misted. Most commercially available lady beetles are convergent lady beetles, as they are easily collected in large numbers from overwintering sites. It may take a couple weeks after release in optimal conditions for them to become fully active predators.

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Parasitoid Wasps

The parasitoids in the subfamily Aphidiinae are small wasps (0.08 – 0.12 inches). Some species are commercially available for aphid control. Adult wasps lay eggs inside of aphid hosts. The eggs hatch inside aphids and the larvae begin to feed on aphid tissue. In later development, the larvae kill the aphids and pupate inside the mummies. They exit the aphids as mature wasps.

Commercially available parasitoids are within the genera Aphidius (Hymenoptera: Braconidae) and Aphelinus (Hymenoptera: Braconidae). Like predators, parasitoids are most effective when aphid populations are low. However, in certain systems, it has been demonstrated that using both predators and parasitoids together is more effective than using one or the other [14. 15].

Aphidius colemani

These parasitoids are effectively used in glasshouses and outdoors in temperate regions. Ideal conditions are 70-77°F and relatively high humidty (~80%). Temperatures above 85°F halt parasitoid development, but in 50°F temperatures, parasitoids may still develop. Humidity is relatively less important, and development may still occur even in low humidity. If the humidity is sufficient for They are sold as aphid mummies from which wasps emerge or as newly emerged adults. They are useful in the winter because they are not affected by short days, but aphids are generally not a problem in cold weather anyways. They are commonly used for control of M. persicae, but have also been observed to parasitize the more feared and recently introduced cannabis aphid (Phorodon cannabis).

A. ervi

This is another parasitoid that has been found to complete its life cycle using P. cannabis as the host. Life cycle and environmental conditions are similar to A. colemani

Aphid Midge (Aphidoletes aphidimyza)

These midges are cecidomyiid flies that are effective aphid predators. Like green lacewings, it is the larvae that feed on the aphids. It is common to release aphid midges along with green lacewings to increase predator diversity, as each predator may fill different niches better. Adults are small (2-3mm) and resemble mosquitos, while larvae look like small orange maggots that can also reach 2-3mm in size. Eggs are laid in foliage, and the larvae begin feeding on aphids on the plants after hatching, then they drop to the soil within a week to pupate. Larvae can eat up to 80 aphids but require at least 7 to complete the life cycle [27]. These midges are less affected by azadirachtin than green lacewings. While green lacewings larvae are not killed by azadirachtin, it may interfere to some degree with the egg-laying of female lacewings. For this reason, it may be worth it to use midges either in place of or supplementary to release of lacewings if you are also using neem or azadirachtin [28]. They will go in to diapause if the day length drops below 12 hours or temperatures are below 50 farenheit. They require soil and will not work in hydroponic systems [29].

Minute Pirate Bugs (Orius insidiosus)

Beware! These insects have a painful bite. They are good generalist predators that do well with controlling thrips and aphids. They reproduce fairly quickly, completing their life cycle in under a month. They do well at temperatures between 64-82°F, with 60% RH. It is recommended to release 100-2000 per acre depending on pest population.

Most beneficial insects are not available on Amazon. Check out Arbico Organics at arbico-organics.com

Chemical Control

Azadirachtin and Neem Oil

Both neem oil and azadirachtin are effective in controlling various aphid species, but the efficacy of the compounds varies depending on the aphid species [17]. It appears that insecticidal activity is not due to antifeedant activity, but instead inhibits reproduction and molting. Neem appears relatively harmless to many beneficial insects and can usually be used along with other strategies. When utilizing fungal biocontrol such as B. bassiana or I. fumosorosea, azadirachtin may be more compatible than complex mixtures such as neem oil.

Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil – (16 oz) High Azadirachtin Content – OMRI Listed for Organic Use

Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil 32 oz – OMRI Listed for Organic Use

General Hydroponics GH2045 AzaMax, 4 Ounce

General Hydroponics AzaMax, 16 oz GH2007

Insecticidal Soaps

The active ingredients of these soaps are potassium salts of fatty acids. The soap is able to disrupt the cuticle of the insect, essentially leading to death through desiccation. They are contact pesticides that have no residual pesticidal activity. They are also very broad spectrum pesticides and will kill beneficial insects as well as pests. Because of this, it is not recommended to use insecticidal soaps concurrently with beneficial insect release. However, they can be used as a useful knock down spray to reduce initial populations. Water sprays can be effective at reducing the populations just by knocking aphids of the plants, but using insecticidal soaps ensures that aphids knocked off do not find their ways back to the plants. Soaps can also be mixed with other insecticides including pyrethrins, horticultural oil, essential oils, triglycerides, or azadirachtin and neem products. While good as a part of an IPM program, neem oil and azadirachtin are not as effective against P. humuli as pyrethins, insecticidal soaps, or beneficial fungi [18]. Based on anecdotal evidence, I believe neem is less effective on P. cannabis than on some other aphid species, but should still be used preventatively or tank mixed with other insecticides as a knock down treatment.

Safer Brand 5118-6 Insect Killing Soap Concentrate 16oz

Natria 706230A Insecticidal Soap Organic Miticide, 24 oz, Ready-to-Use

Safer Brand 5110-6 Insect Killing Soap, 32 oz.


Pyrethrins are insecticides found in some chrysanthemum. Due to the source, they can be used in organic production. Usually, formulations have six chemicals found in the flowers. They are non-persistent and typically degrade within a few days when exposed to the environment and sun. Synthetic pesticides called pyrethroids have been made that mimic the activity of pyrethrins, do not degrade readily, but are not approved for use in Cannabis. Pyrethrins are much lower risk than pyrethroids for both consumer health and meeting pesticide testing limits. However, there have been reports of flower failing residue limit tests of pyrethrins and it is not fully understood why. Piperonyl butoxide (PBO) can be mixed with pyrethrins as a synergist. PBO works by inhibiting insect enzymes that may help break down pyrethrins. Pyrethrins are quite effective as an initial knockdown.

PyGanic Gardening 8oz, Botanical Insecticide Pyrethrin Concentrate for Organic Gardening

Pyrethrins can be mixed with insecticidal soaps or neem products such as azadirachtin

Safer Pyrethrin & Insecticidal Soap Concentrate, 1 Gallon

Azera Gardening 8 oz, Botanical Dual Action Azadirachtin/Pyrethrin Fast-Acting Insecticidal Concentrate for Organic Gardening.

Horticultural Oils (Triglycerides, Mineral Oil, Essential Oils)

Most horticultural oils, particularly mineral oils and plant fat oils, work by suffocating insects and blocking respiration. Mineral oils are composed of higher alkanes derived from petroleum, and plant oils are mainly triglycerides. Triglycerides are composed of a glycerol molecule bound to three fatty acids which may be saturated or unsaturated. Most horticultural oils are most effective when mixed with a surfactant that helps spread the oils and may help deliver the oils more effectively to insect spiracles. Horticultural oils are also quite effective against fungi, particularly epidermal-limited pathogens such as powdery mildew.

Plant oils tend to be harsher on the plant epidermis than refined mineral oils and can more easily result in leaf burn. However, many plant oils contain other fat-soluble secondary metabolites that may have insecticidal activity. For instance, neem oil contains azadirachtin which inhibits insect reproduction and molting, but it also has triglycerides that work through suffocation. Other common plant oils used as insecticides include corn oil, soybean oil, canola oil, and other vegetable oils.

Various plant-derived essential oils can also have insecticidal activity. Essential oils can be derived in a variety of ways, most frequently by steam distillation followed by separation of the non aqueous layer or by solvent extraction. Steam distillation results in a high concentration of low molecular weight, nonpolar, volatile (easily becomes gaseous) chemicals including small terpenes, aldehydes, alcohols, and esters. Fatty acids are not easily recovered through distillation. Solvent extraction with nonpolar solvents such as hexane can also recover these chemicals, but during the solvent removal, many of the smaller volatiles may be lost and larger nonpolar molecules may remain. Essential oils also can be present in cold press extracts along with fatty acids.

One such essential oil product is Trifecta Crop Control. Along with essential oils, the product contains corn oil, citric acid, and an emulsifier. According to the Trifecta website, Trifecta works through more complex mechanisms than simply suffocation: clove oil contains eugenol: a terpene that causes cell lysis in fungal species, peppermint oil for reproductive inhibition, garlic oil for repellency and to treat systemic fungal infections, thyme oil for endocrine disruption in soft body pests, corn oil as a suffocant, and citric acid for chelating calcium in insect’s exoskeletons [19].

Trifecta Crop Control Super Concentrate All-in-One Natural Pesticide, Fungicide, Miticide, Insecticide, Eliminate Spider Mites, Powdery Mildew, Botrytis, Mold and More on Plants Non-Toxic 4oz

Monterey LG 6299 Horticultural Oil Concentrate Insecticide/Pesticide Treatment for Control of Insects, 32 oz

IPM Concepts

If you wish to avoid chemical control altogether, it is possible to achieve good levels of prevention using predator insects and parasitoids. It is generally recommended to use both parasitoids and insects within the generalist predator guild. For instance, weekly to biweekly release of green lacewings (5,000-10,000 eggs/acre) and parasitoid Aphidius species (500 aphid mummies/acre) can provide good control and release numbers can be increased up to tenfold at the first sign of infestation. Other insects that can be purchased and released are convergent lady beetles (Hippodamia convergens) and minute pirate bugs (Orius insidiosus).

Compared to many synthetic insecticides, neem and azadirachtin products tend to be relatively benign to beneficial insect populations [17]. Undoubtedly, neem has negative effects on the total predator population, but the number of surviving predators relative to the number of surviving aphids is not significantly different, and the aphid parasitism rate by Aphidius can actually increase [17]. However, it is important to mitigate the negative effects of neem on predators by using proper application timing. For instance, spraying neem 24 hours before predator release will allow for the knockdown effect of neem while preventing the predators from coming in to direct contact with the neem. If releasing predators on a biweekly basis, neem can also be sprayed at the same frequency but one day prior to release. If you alternate between release and neem on a weekly basis, or if you spray neem directly after predator release, you can negatively effect the predator populations [20].

In regards to entomopathogenic fungi, B. bassiana is fairly similar to neem in that it has little effect on beneficial insects if it is sprayed before release of beneficials. B. bassiana can colonize some host plant endophytically, and the predatory effects of green lacewings does not appear to be negatively affected by feeding on aphids that have been sprayed with B. bassiana spores or aphids that are feeding on plants that have been endophytically colonized by B. bassiana [21]. However, spraying green lacewings directly with B. bassiana spore suspensions can negatively affect lacewing populations [22]. B. bassiana may be incompatible with lady beetles as well. Therefore, it is a good idea to time applications to minimize off target effects. One study that looked at the timing of B. bassiana in relation to release of parasitoid A. colemani demonstrated that ideal B. bassiana spray timing is approximately 3 days after M. persicae parasitism by A. colemani. There is speculation that immature parasitoids may produce fungistatic or fungicidal metabolites to prevent the entomopathogenic fungi from killing the hosts. Furthermore, aphids colonized by B. bassiana prior to oviposition by parasitoids appear to reduce the success of parasitoids [22].

B. bassiana can infect minute soldier bugs quite well, as well as convergent lady beetles, but it can be feasibly used with lacewings and parasitoids by using a timing such as the following:

Infestation Response:

  1. At first sign of aphid infestation, do a knockdown spray with a product such as pyrethrins (recommended for Cannabis aphid), or pyrethrins mixed with insecticidal soap.
  2. When dry, release parasitoid Aphidius wasps (up to 4,000/acre depending on population). These are high release rates and in most cases, fewer should be sufficient.
  3. 4-5 days after wasp release (if using adults), spray with B. bassiana product such as Botanigard
  4. After dry, release green lacewings up to 10,000 per acre, aphid midges, and up to 5,000 minute pirate bugs/acre, depending on populations. This is only in severe infestations, even half of these numbers should be sufficient for more infestations.


  1. Do weekly release of predators and parasitoids at lower levels of 400 wasps, 200 minute pirate bugs, 1,000 lacewings, and 1,000 aphid midges per acre to suppress levels. This is a mixture of 4 good beneficials, but you can cut back to parasitoid wasps and one or two of the predators rather than using all of them.
  2. Use a rotation of Grandevo, Venerate, and Neem Oil. A rotation of any 2 products in this list could also be used. Both Grandevo and Venerate do not affect beneficial insects, and neem oil has low toxicity that can be mitigated with proper application timing.

If you do not want to use pyrethrins as a knockdown, I would recommend using a product such as Trifecta that contians an insecticidal soap, citric acid, essential oils, and corn oil. Please do not use Spinosad or synthetic pesticides in commercial operations as they are not labeled for use in Cannabis and are tested for.

Isaria fumosorosea may be even more effective than B. bassiana, at least in the case of M. persicae [24], and is of similar effectiveness as B. bassiana on the hop aphid (Phorodon humuli), closely related to P. cannabis [26]. For all applications of B. bassiana, it may be worth either trying I. fumosorosea or rotating between application of B. bassiana and I. fumosorosea. For both of these fungi, high humidity is ideal and ambiet humidity should not be below 50%, with higher humidities being more effective.

  1. Dedryver, C.-A., Le Ralec, A., & Fabre, F. (2010). The conflicting relationships between aphids and men: A review of aphid damage and control strategies. Comptes Rendus Biologies, 333(6), 539–553. https://doi.org/https://doi.org/10.1016/j.crvi.2010.03.009
  2. APHIDS: What You Want to Know About Them and How to Organically Get Rid of an Aphid Infestation in Your Cannabis — Ed Rosenthal. (n.d.). Retrieved April 21, 2020, from https://www.edrosenthal.com/the-guru-of-ganja-blog/aphids-what-you-want-to-know-about-them-and-how-to-organically-get-rid-of-an-aphid-infestation-in-your-cannabis
  3. McPartland, J. M., Clarke, R. C., & Watson, D. P. (2000). Hemp
  4. diseases and pests: management and biological control: an advanced treatise. CABI.
  5. Shannag, H. K., & Capinera, J. L. (2018). Comparative Effects of Two Novel Betaproteobacteriabased Insecticides on Myzus persicae (Hemiptera: Aphididae) and Phenacoccus madeirensis (Hemiptera: Pseudococcidae). Florida Entomologist, 101(2), 212–218. https://doi.org/10.1653/024.101.0209
  6. OREGON DEPARTMENT OF AGRICULTURE FACT SHEETS AND PEST ALERTS. (n.d.). Retrieved April 26, 2020, from http://www.Oregon.gov/ODA
  7. Kim, J. J., Jeong, G., Han, J. H., & Lee, S. (2013). Biological Control of Aphid Using Fungal Culture and Culture Filtrates of Beauveria bassiana. Mycobiology, 41(4), 221–224. https://doi.org/10.5941/MYCO.2013.41.4.221
  8. Endophytic Beauveria bassiana negatively impacts green peach aphids on strawberries – E-Journal of Entomology and Biologicals – ANR Blogs. (n.d.). Retrieved April 26, 2020, from https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=21711
  9. Sayed, S. M., Ali, E. F., & Al-Otaibi, S. S. (2019). Efficacy of indigenous entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin, isolates against the rose aphid, Macrosiphum rosae L. (Hemiptera: Aphididae) in rose production. Egyptian Journal of Biological Pest Control, 29(1), 19. https://doi.org/10.1186/s41938-019-0123-y
  10. Rashki, M., & Shirvani, A. (2013). Taxonomy of Noctuidae family View project. https://www.researchgate.net/publication/237843387
  11. Dorschner, K. W., Feng, M.-G., & Baird, C. R. (1991). Virulence of an Aphid-Derived Isolate of Beauveria bassiana (Fungi: Hyphomycetes) to the Hop Aphid, Phorodon humuli (Homoptera: Aphididae) . Environmental Entomology, 20(2), 690–693. https://doi.org/10.1093/ee/20.2.690
  12. Hunter, W. B., Avery, P. B., Pick, D., & Powell, C. A. (2011). Broad Spectrum Potential of Isaria fumosorosea Against Insect Pests of Citrus. Florida Entomologist, 94(4), 1051–1054. https://doi.org/10.1653/024.094.0444
  14. Avery, P., Pick, D., Aristizábal, L., Kerrigan, J., Powell, C., Rogers, M., & Arthurs, S. (2013). Compatibility of Isaria fumosorosea (Hypocreales: Cordycipitaceae) Blastospores with Agricultural Chemicals Used for Management of the Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae). Insects, 2013, 694–711. https://doi.org/10.3390/insects4040694
  15. Rocca, M., & Messelink, G. J. (2017). Combining lacewings and parasitoids for biological control of foxglove aphids in sweet pepper. Journal of Applied Entomology, 141(5), 402–410. https://doi.org/10.1111/jen.12355
  16. Gontijo, L. M, Beers, E. H, & Snyder, W. E. (2015). Complementary suppression of aphids by predators and parasitoids. Biological control, 90, 83-91. doi: 10.1016/j.biocontrol.2015.06.002
  17. Schreiner, M. (2019). A survey of the arthropod fauna associated with hemp (0RW1S34RfeSDcfkexd09rT2cannabis sativa1RW1S34RfeSDcfkexd09rT2 L.) grown in eastern colorado (Order No. 27546665). Available from ProQuest Dissertations & Theses A&I. (2379078782). Retrieved from https://search.proquest.com/docview/2379078782?accountid=14505
  18. Lowery, D. T., & Isman, M. B. (1994). Effects of Neem and Azadirachtin on Aphids and Their Natural Enemies. In Bioregulators for Crop Protection and Pest Control (Vol. 557, pp. 7–78). American Chemical Society. https://doi.org/doi:10.1021/bk-1994-0557.ch007
  19. Vasilev, P., Atanasova, D., & Andreev, R. (2019). Efficacy of Bioinsecticides against the Hop Aphid Phorodon Humuli (Schrank) (Hemiptera: Aphididae) under Laboratory Conditions. Canadian Journal of Agriculture and Crops, 4, 130–135. https://doi.org/10.20448/803.
  20. Official Home Of Trifecta Crop Control: Defeat Mold Mildew and Fungus. (n.d.). Retrieved April 30, 2020, from https://www.trifecta.com.bz/
  21. Medina, P., Smagghe, G., Budia, F., Tirry, L., & Viñuela, E. (2003). Toxicity and Absorption of Azadirachtin, Diflubenzuron, Pyriproxyfen, and Tebufenozide after Topical Application in Predatory Larvae of Chrysoperla carnea (Neuroptera: Chrysopidae) . Environmental Entomology, 32(1), 196–203. https://doi.org/10.1603/0046-225x-32.1.196
  22. González-Mas, N., Cuenca-Medina, M., Gutiérrez-Sánchez, F., & Quesada-Moraga, E. (2019). Bottom-up effects of endophytic Beauveria bassiana on multitrophic interactions between the cotton aphid, Aphis gossypii, and its natural enemies in melon. Journal of Pest Science, 92(3), 1271–1281. https://doi.org/10.1007/s10340-019-01098-5
  23. Portilla, M., Snodgrass, G., & Luttrell, R. (2017). Lethal and sub-lethal effects of Beauveria bassiana (Cordycipitaceae) strain NI8 on Chrysoperla rufilabris (Neuroptera: Chrysopidae). Florida Entomologist, 100(3), 627–633.
  24. Emami, F., Alichi, M., & Minaei, K. (2013). Interaction between the entomopathogenic fungus, Beauveria bassiana (Ascomycota: Hypocreales) and the parasitoid wasp, Aphidius colemani Viereck (Hymenoptera: Braconidae). Journal of Entomological and Acarological Research45(1), e4. https://doi.org/10.4081/jear.2013.e4
  25. Meng, H., Tian, J., Fu, S., Diao, H., & Ma, R. (2014). Pathogenicity of Isaria fumosorosea and Beauveria bassiana against the green peach aphid, Myzus persicae. Acta Phytophylacica Sinica, 41(6), 717–722.
  26. Dorschner, K. W., Feng, M.-G., & Baird, C. R. (1991). Virulence of an Aphid-Derived Isolate of Beauveria bassiana (Fungi: Hyphomycetes) to the Hop Aphid, Phorodon humuli (Homoptera: Aphididae) . Environmental Entomology, 20(2), 690–693. https://doi.org/10.1093/ee/20.2.690
  27. Mohammed, A. A., Kadhim, J. H., & Kamaluddin, Z. N. A. (2018). Selection of highly virulent entomopathogenic fungal isolates to control the greenhouse aphid species in Iraq. Egyptian Journal of Biological Pest Control, 28(1), 71. https://doi.org/10.1186/s41938-018-0079-3
  28. Aphidoletes aphidimyza. (n.d.). Retrieved May 3, 2020, from https://biocontrol.entomology.cornell.edu/predators/Aphidoletes.php
  29. Azadirachtin & Neem Oil. (n.d.). Retrieved May 3, 2020, from https://www.growertalks.com/Article/?articleid=23465
  30. Aphidoletes for Aphid Control. (n.d.). Retrieved May 3, 2020, from https://greenmethods.com/aphidoletes/
  31. Insects/Mites that Feed on Hemp – Fluid Feeders: Cannabis Aphid. (n.d.). Retrieved May 5, 2020, from https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Cannabis aphid August 2018 revision.pdf
  32. SYSTEMATIC TREATMENT OF APHID GENERA. (n.d.). Retrieved May 5, 2020, from http://www.aphidsonworldsplants.info/d_APHIDS_A.htm#Abstrusomyzus

Mites affecting Cannabis

Mites are probably the most feared arthropod pests of Cannabis. There are three types of mites that are of particular concern for Cannabis growers: broad mites, russet mites, and spider mites. Spider mites are the most widespread and pervasive issue, but broad mites and russet mites are harder to deal with and can result in devastating losses.

What is a mite?

A mite is an arachnid in the subclass Acari (Phylum Euarthropoda, Class Arachnida). Acari also contains ticks, but ticks are not included in the mite classification. Mites are quite small and the majority are under 1mm in length.

Not all mites are pests

Mites span a large range of lifestyles. Many mites are integral parts of the soil food web and act as decomposers of organic matter. In forest soils, up to 400,000 mites can be found in a square meter of soil [1]. Some mites act as predators or parasites and may feed on other arthropods or fungi. Some of these mites are used in biological methods for controlling pest populations. A small number of mites actually pose a substantial risk to plants.

Spider Mites

Spider mites are within the family Tetranychidae which contains about 1,200 known species [2]. Spider mites feed on plant cells, and they spin webs over plants for protection and transportation.

What Species of Spider Mites Infest Cannabis?

Reportedly, two species of spider mites cause the most damage on Cannabis plants, the two-spotted spider mite Tetranychus urticae and the carmine spider mite T. cinnabarinus [3]. Both species are very similar in their life cycles and appearance, but T. cinnabarinus thrives in higher temperatures than T. urticae and vice versa for cooler temperatures [3]. Generally speaking, T. urticae only causes significant damage in semi-tropical regions with temperatures above 34°C [3].

T. urticae Identification, Symptoms, and Signs

Adult spider mite identification

  • Adults are very small (about 0.4 mm in length), and males are slightly smaller than females. They are straw-colored to green and have large dark spots on either side of the abdomen
Image adapted from Insects/Mites that Feed on Hemp-Fluid Feeders. (n.d.). Retrieved April 4, 2020, from https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Twospotted spider mite with photos.pdf

Other signs of spider mite infestation (not including visualization of adults)

  • Females lay eggs on the undersides of leaves. Eggs are large in relation to the female (around 0.14 mm) and can be used as indicators of spider mite infestation. Frass (exrement) can also accumulate on leaf tissue.
  • Adults weave extensive webs on the plants that are commonly the first indicators that growers notice on their plants. This webbing can help protect them from predators and can facilitate movement.
Extreme spider mite damage - marijuana colas are literally covered in spider mite webs
Image retrieved from https://growingexposed.com/cannabis-doctor/spider-mites/ on 4/4/2020
Image adapted from Insects/Mites that Feed on Hemp-Fluid Feeders. (n.d.). Retrieved April 4, 2020, from https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Twospotted spider mite with photos.pdf

Plant tissue damage and symptoms from feeding

Spider mites feed on plant cells with stylet-like mouthparts, ‘sucking’ out cell contents and causing cell death.

  • Stippling is a leaf pattern of numerous tiny necrotic specks (aka ‘flecking’). Stippling is usually concentrated on the undersides of leaves, but should also be apparent on the tops of leaves. Feeding on one side of the leaf can cause stippling on the opposite side as well.

Stippling begins with a small amount of greyish specks

Image adapted from Insects/Mites that Feed on Hemp-Fluid Feeders. (n.d.). Retrieved April 4, 2020, from https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Twospotted spider mite with photos.pdf

The greyish stippling continues to spread across the leaf, and the leaves start to become yellowish, copper-brown, and in heavy infestations, can even die.

Image adapted from Insects/Mites that Feed on Hemp-Fluid Feeders. (n.d.). Retrieved April 4, 2020, from https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Twospotted spider mite with photos.pdf

Spider Mite Life Cycle

Life cycle
Image adapted from Managing spider mite on soybean. (n.d.). Retrieved April 4, 2020, from https://extension.umn.edu/soybean-pest-management/managing-spider-mite-soybean#overview%3A-two-spotted-spider-mites-1432910

The life cycle of spider mites is fairly straighforward. After hatching from an egg, the spider mite goes through three instars and molting cycles before reaching adulthood. In optimal conditions (high heat (81°F-86°F) and low humidity), the entire life cycle can be completed in just over a week [4], whereas lower temperatures (60°F-64°F) can slow the life cycle turnover by up to three times (20+ days) [7].

Effects on yield and quality

You may wonder why it is a big deal for plants to be infested.

  1. Appearance- Stippling and bronzing can occur on both sugar leaves and flower calyxes, leading to lower bag appeal. Webbing is also hard to remove and would likely be present in your final product.
  2. High Stress and Lower Productivity- As spider mites kill leaf cells and disrupt the plant cuticle, plants begin to lose control over local transpiration rates. Not only will this lead to lower growth rates and yield, it can lead to symptoms that may commonly appear to be severe drought such as leaves becoming dry and brittle. The numerous necrotric areas result in a lower total photosynthetic rate due to loss of photosynthetically active cells. Yield losses can reach 50% in heavily infested fields [3].

Favorable Environmental Conditions

Optimal environmental conditions for spider mites are high temperatures (30°C ideal) and low humidity [6]. In Farenheit, high 80s is ideal, but temperatures above 90°F may prove inhibitory. I can not find sources on exact RH levels that benefit or inhibit the spider mites, but all publications that I have come across say that low humidity favors spider mites and high humidity inhibits spider mites. However, the humidity levels in most grow rooms that follow vapor pressure deficit guidelines are not excessively high (40%-65% depending on leave temperatures and life cycle stage) and I would certainly recommend following VPD guidelines over running excessively high RH due to prevent issues with bud rot.

Hemp Russet Mite (Aculops cannabicola)

Russet mites are more inconspicuous that spider mites. In very low populations, they don’t cause visible symptoms [8]. In higher populations, symptoms begin to show on plants. In 1965, they were reported in central Europe, and in Kansas in 1971. They are now fairly ubiquitous in the United States and has been a big problem on the west coast for a few years now.


  • *russet mites suppress JA-related plant defenses with compounds introduced to the plant through feeding [17]*
  • A common symptom on Cannabis is a pervasive and conspicuous upward curling of leaf edges. However, this does not always happen depending on cultivar, environment, and infestation severity [8].
Image retrieved from Pest Management of Hemp in Enclosed Production Hemp Russet Mite. (n.d.). Retrieved April 4, 2020, from https://webdoc.agsci.colostate.edu/hempinsects/PDFs/Hemp Russet Mite Revision July 2018).pdf
  • Leaves can become glossy and blistered, almost appearing wet. Interveinal regions can turn a crimson-like color (russeting). Some of these symptoms may be misdiagnosed as Hemp Streak Virus (HSV).
Image retrieved from https://www.greenboxgrown.com/russet-mites
  • As symptoms progress, leaves become brittle, dry, and more russeted, eventually leading to leaf death. Leaves may break off at the petiole.
Image adapted from https://www.growweedeasy.com/wp-content/uploads/2017/10/broad-mites-cannabis-1.jpg
  • Russet mites can also infest plant stems and cause visible masses, especially near cola tops. This can result in wilting and even death of plant tops. They can even feed on flower petioles, leaving female flowers sterile [8].
Images retrieved from https://www.growweedeasy.com/cannabis-plant-problems/hemp-russet-mites

Identifying Adult Russet Mites

  • Russet mites are less than half the size of spider mites (0.2 mm long) and may need magnification to visualize [9]. 60x magnification is ideal.
  • Unlike many arachnids, Russet mites have 2 pairs of legs instead of 4.
  • They are soft-bodied, quite pale, and have 2 segments, the gnathosoma (mouth parts) and the idiosoma (the rest of the body).
Hemp Russet mites - YouTube
Image adapted from https://www.youtube.com/watch?v=Aui0ZIu5zuE
Image adapted from https://www.youtube.com/watch?v=0Uz_Cp_LwNE

Life Cycle

  • One publication says that the life cycle of the hemp russet mite at 27°C and 70% RH takes 30 days [8]. However, there is no study cited for this claim, and most other resources have vastly shorter estimations. This estimation is likely quite off.
  • Most eriophyid mite species share a similar life cycle that includes the egg, two nymphal instars, and the adult [9]. Almost all eriophyid mites complete their life cycle in approximately 7 days [9].
  • Females can overwinter in plant debris, especially in plant stems and petiole bases.
Maple Bladdergall Mite | NC State Extension Publications
Image retrieved from https://content.ces.ncsu.edu/maple-bladdergall-mite

Favorable Environmental Conditions

Generally speaking, russet mites can proliferate at lower temperatures than spider mites. In a study on the tomato russet mite, the ideal environmental conditions for proliferation were found to be around 80°F and 30% RH [10]. In regards to higher humidity and lower temperatures, another study found that they were able to reproduce in conditions of 15-24 degrees C (59-75 degrees F) and 70-80% relative humidity [11].

Did Cal Trans Cause a Russet Mite Outbreak on the West Coast?!

I want to address this topic because I see a lot of people saying that the Russet Mite outbreak in CA was due to Cal Trans releasing mites for control of thistles. This idea is based on the .pdf file Enhanced Biological Control of Yellow Starthistle and Tumbleweed (Russian Thistle) by the Department of Transportation [12], which discussed the use of a blister mite, Aceria salsolae as a control agent for invasive Russian thistle. First of all, this mite is not the same as the Cannabis russet mite, it is specific to the Russian thistle. Second of all, the release of these mites was never approved [13]. Hemp russet mites are spreading more rapidly due to higher temperatures, and can be quickly spread in an industry such as the Cannabis industry that does not have clean stock programs or good practices related to seed and clone disinfestation.

Broad Mites (Polyphagotarsonemus latus)


Like russet mites, broad mites adults are around 0.2 mm in length, and the eggs are under 0.1mm. You will not be able to see them with the naked eye. The best magnification to see them with is about 60x. Unlike russet mites, they tend to reside only in new leaves and don’t feed on fully opened leaves. However, they tend to be quite pale, almost transparent, but slightly greenish-goldish. They have two pairs of front legs, a pair in the middle of the abdomen, and a whispy pair of leg-like appendages in the back. Broad mites can walk short distances, but can also be wind-borne or attract and hitch rides on other insects including aphids and whiteflies [16]. You will often only find broad mites in new apical leaves because they can hide easier and feed on young tissue that has not developed as many defenses [15].

Photographs of a female broad mite, Polyphagotarsonemus latus (Banks), on the surface of a pepper leaf. The (views from top to bottom: dorsal, left lateral, right lateral, front, rear) photographs were taken with a low temperature scanning electron microscope. The specimen was held on a new, height-angle, azimuth rotation specimen holder and frozen in its natural position with liquid nitrogen. The USDA has a Build-A-Mite Web site where these five photographs can be copied, cut and folded to create a box that depicts the mite's three-dimensional shape.
Image from http://entnemdept.ufl.edu/creatures/orn/broad_mite.htm
broad mite on fruit
Image from https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11677

Life Cycle

The life cycle is basically the same as the russet mite of which there is a diagram in that section. There is an egg, a larva, a nymph, and an adult.

Each female can lay 40-50 eggs. It takes about 2 days for eggs to hatch, and
the larval and pupal development takes 2-3 days. Males hatch first and carry female pupae to young tissues. Females mate right away, but if they do not mate, they will still lay eggs in an asexual manner to all male mites. The male mites can then may mate with the female for sexual production to occur (same genes but recombination occurs). In optimal conditions, the life cycle takes about a week. They generally reproduce and reside in new developing leaves and are rarely found on fully opened leaves [15].


The symptoms can be indistinguishable from russet mite damage. In my opinion, broad mites tend to cause the leaves to curl down more than russets but the very edges of the leaves tend to ‘taco’ in both cases. Leaves tend to be a bit more deformed because broad mites secrete a toxin in their saliva that affects newly developing leaves [15].

Image adapted from https://www.growweedeasy.com/cannabis-plant-problems/broad-mites

Ideal Environment

Broad mites thrive in warm temperatures, but indoors they can be active year round [15]. Unlike russet mites and spider mites, broad mites thrive in high humidity (80% is ideal). In regards to temperature, the optimum temperature for broad mite reproduction is 30°C (86°F) with close to 100% survival from egg and about a 3.5 day development period to adulthood. Over 90°F begins to be inhibitory (20-30% survival rate from egg to adulthood), although development time is still fast at this temperature (4-5 days). Lower temperatures (around 60°F have survival rates around 30% but have long development times of almost 2 weeks) [18]. Humidity under 60% RH will help control broad mites.n Unlike russet mites, broad mites don’t overwinter in plant stems or the soil and may not survive in cold regions over the winter.

Image adapted from Columbia Ministry of Environment, B., & Change Strategy, C. (2019). Integrated Pest Management for Commercial Cannabis in BC.

How To Prevent and Treat Mite Infestations

The first concept I want to get across is that an ounce of prevention is worth a pound of cure. If you are in an area that has problems with any of these mites, you should have an IPM program in place to prevent them from infesting your plant. There are a broad range of ways to do this, including pesticide sprays, or beneficial fungi and predator mites.

Predator Mites

This method has a lot of benefits, especially preventatively or in flower when you are avoiding sprays.

Amblyseius cucumeris.

This mite thrives best in conditions similar to the broad mite. It can stand a wide range of temepratures from 20°C to 30°C. It prefers humid conditions of 70%-80% RH, but can still complete its life cycle well at 40% RH if it is kept cooler [19]. However, keeping RH above 50% is highly recommended. It is a good choice for IPM because it is very aggressive on thrips, but can also feed on stages of russet mites, broad mites, and spider mites. They need pests to feed on, so if they control your problem, they will begin to decline in population. There are slow release packets available that will release mites from a packet with a bran substrate for the bran mites that act as a temporary food source. A packet works well for about a month.


1,000 Live Neoseiulus Amblyseius Cucumeris – Guaranteed Live Delivery!

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Mites on carrier for sprinkling on plants:

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Amblyseius californicus

This mite primarily feeds on spider mite populations and can also feed on microscopic mites such as russets, broad mites, and cyclamen mites. They thrive well in any Cannabis growing environment. They can tolerate wide ranges of heat (10°C-33°C) and humidity, and can even survive short periods of under freezing temperatures. They do well in humidity levels of 40%-80%, which falls within the common ranges used to follow VPD recommendations in indoor grows. They do prefer humidity on the higher ends [19]. They do especially well in environments that get hot and low humidity. Satchets can be ordered for this mite as a preventative for various mites or can be applied at first sign of spider mite infestation.

Mites on Carrier:

Nature’s Good Guys 2,000 Live Adult Predatory Mites Packed in a 16 oz Container – P. persimilis a Predatory Mite Species for Spider Mite Control – Ships Next Business Day!

5,000 Live Adult Predatory Mites – Neoseiulus (Amblyseius) Californicus a Predatory Mite Specie for Spider Mite Control – Ships Next Business Day!l

Amblyseius swirskii

This is probably one of the best choices for controlling broad mites, russet mites, and cyclamen mites. It is a fairly broad predator and also feeds on spider mites, thrips, and whiteflies. At 60% RH, mites develop between 18°C and 36°C, though for good activity the daytime temperature should be above 22°C [21]. Optimum temperatures are around 25-28 °C. These mites can be used at higher temperatures than A. cucumeris provided RH remains high on leaf surface. Unlike A. californicus, they have poor tolerance to freezing temperatures. A. swirskii prefers high humidity and does not do as well as A. californicus with low humidity.


Nature’s Good Guys Amblyseius swirskii 25 Sachets with 250 Mites

Amblyseius Swirskii (25,000 in Hanging Sachets)

Amblyseius andersoni

This is one of the best choices for targeting mites specifically. They prefer feeding on mites over thrip larvae and feed on spider mites, cyclamen mites, broad mites, and russet mites. It has an extremely large active humidity range of 6-40ºC. These mites are also very good preventatives for pest mites because they can survive on fungi and honedew as well. A slow release satchet will provide about a month of protection and maybe more depending on if the population can persist on other food sources in your environment. They can survive in some lower humidities (at 20ºC, when the mites are actively feeding, there is about a 50% survival rate to adulthood at 50% RH). These mites should not be used in grow areas with humidity below 50% RH.

Order from mite supplier- not available on Amazon

Galendromus occidentalis

This is another mite-targeting species that feeds on all the types of mites discussed in this article. These mites love hot temperatures (27-43ºC) and may go in to hibernation in daytime temperatures under 27ºC. It can tolerate high humidity, but is most effective in RH between 30 and 60% RH [22]. However, it can tolerate even lower humidities. it is a great choice for particularly dry glasshouses that may have below 40% RH. However, it does not do well in cold temperatures.

Order from mite supplier- not available on Amazon

Phytoseiulus persimilis

This predatory mite is specifically useful for the two spotted spider mite and specifically feeds on web-weaving mites, but not so much against the microscopic foliage mites. The are about a half millimeter long and are striking orange. It controls the two-spotted spider mite at temperatures from 15°C to 27°C with humidity from 60% to 90%. Ideal conditions for control are obtained at 27°C (around 80°F) and 60%–85% R.H. At lower temperatures of 21°C (70°F), control can be obtained at humidity down to 40%, but at higher temperatures of 27°C, 40% RH is too low for effective control [31]. Time to adulthood can range from 25 days at 15°C to 5 days at 30°C. At ideal temperatures and RH levels, generation times are typically around a week [32].

Mites on Carrier

Nature’s Good Guys 2,000 Live Adult Predatory Mites Packed in a 16 oz Container – P. persimilis a Predatory Mite Species for Spider Mite Control – Ships Next Business Day!

Nature’s Good Guys 20,000 Live Adult Predatory Mites – P. persimilis a Predatory Mite Species for Spider Mite Control – Ships Next Business Day!

Nature’s Good Guys 10,000 Live Adult Predatory Mites – P. persimilis a Predatory Mite Species for Spider Mite Control – Ships Next Business Day!

Entomopathogenic Fungi and Bacteria

Some fungi have adapted to infect, colonize, and consume living insects. Entomopathogenic means disease-causing on insects. Mites are not insects, but some of these fungi also actively kill and colonize mites. I believe these products are quite useful in the battle against aggressive microscopic foliar mites.


Beauveria bassiana strain GHA

B. bassiana spores germinate and infect mites through their cuticle. Infection is usually lethal within a few days.

  • One study found up to 49.5% mortality of two-spotted spider mites within 4 days and did not affect any predatory mites tested [25]. It may negatively affect some predatory mite species such as A. swirskii depending on spray timing and development stages but not affect other species such as A. cucumeris [46, 47]. In tomato russet mites, B. bassiana was particularly effective at reducing Russet mites as compared to other fungi, azadirachtin, and pyrethrins [26]. In broad mites, B. bassiana can cause over 80% mortality, and was found to be more effective than other tested fungi [27].
  • The ideal environmental condition for fungal pathogenicity is 100% RH and 25-30ºC, but some isolates grow best as low as 20ºC [28]. Spores can become inactive above 30ºC and have very inhibited growth at 15ºC. However, no grower keeps their grow at this humidity level because of other pests and diseases that can be caused at such high temperatures. The fungus is still active at humidity levels down to 30% RH, albeit at a lower rate [28]. Leaf humidity should be at least 60% RH to have a significant effect and the higher the humidity, the more active the fungus.
  • Products include Mycotrol, Botanigard, and Velifer for B. bassiana only sprays. Botanigard Maxx also has pyrethrins in it. According to the manufacturers of Botanigard Maxx, it can be used up to 3 weeks before harvest (in Cannabis).
  • B. bassiana is also useful for controlling vectors of mites such as aphids and whiteflies.
  • B. bassiana may affect beneficial mites some, but in general has been found to be compatible with Amblyseius species.
BotaniGard 22WP Biological Insecticide 1lb

BotaniGard MAXX 32oz. Quart Insect Control Mycoinsecticide

Botanigard ES Insecticide – 1 Gallon

Botanigard Maxx 1 Gallon Beauveria bassiana

Isaria fumosorosea

In a well-controlled environment, this entomopathogenic fungus can effectively kill over 90% of two-spotted spider mite, but may lose effectiveness at high temperatures [33]. It is generally used more for aphids and whiteflies, but may also help with control of various mites. I would not use this as the only biological control in an IPM program, but it may be useful in a rotation with other fungal sprays such as B. bassiana. I have not found studies on the efficacy on broad mites or russet mites, but it is at least demonstrated to be useful on spider mites in particular environmental conditions. Many anecdotes from growers say this is effective on russet mites and broad mites as well and use this in rotation with other biologicals including B. bassiana and C. subtsugae [34].

  • Recommended product is PFR-97 20% WDG
  • Should not be applied within 5 days of fungicide
  • Ideal environment: 80% RH or higher for 8-10 hours when air movement is low and temperatures are 70-90°F [35]. The humdity of the leaf surface is usually much higher than that of ambient air, and so an ambient humidity from 40%-50% may be sufficient if air movement is low. It is best applied in the early evening or morning where light is low, temperatures are lower, and humidity begins to rise outdoors.

Buy from your pesticide provider or from Certis USA. Not available on Amazon

There are some growers I have talked to who have not had success with PFR-97 in field conditions. In fact, the earlier study cited in regards to the effectiveness of PFR-97 does state that in greenhouse, the product did not work to control the spider mites.


Burkholderia spp. strain A396

Burkholderia is a genus of gram negative, obligate aerobic proteobacteria. The genus contains various pathogenic species on a wide range of organisms including plants an animals. This particular strain of a Bulkholderia species is pathogenic on arthropods and in Cannabis is particularly useful against aphids, broad mites, russet mites (can also be used for spider mites), and thrips. It was described as a novel Bulkholderia species isolated from the soil known as Burkholderia rinojensis [30]. It contains various bacterial metabolites, enzymes, and heatkilled bacteria that kill insects using multiple mechanisms of action. In spider mites, over a 90% mortality rate was observed within 3 days of application [30].

  • Venerate CG by Marrone Bioinnovations is a Cannabis-driven product that has a MRL tolerance exemption and a 0 day preharvest interval. There is no limit on application numbers. This is a highly recommended product for both knockdown and prevention of spider mites.
  • Avoid using at the same time as beneficial mites. Give at least 48 hrs between spraying Venerate and releasing mites or beneficial insects.
  • Use with a spreader-sticker such as Oroboost to maximize effectiveness.

Just a heads up: you may be able to buy smaller quantities directly from Marrone Bioinnovations. I will link what is available on Amazon, which is a gallon size.

Marrone Bio Innovations Venerate CG Gallon

Venerate XC Bioinsecticide 2.5 Gallon

OROBOOST 1 Quart. A Registered Material for use in Organic Agriculture. A Versatile Spreader and penetrant for foliar-Applied miticides, insecticides, fungicides, herbicides and Liquid fertilizers.

Chromobacterium subtsugae

Similar to Bulkholderia, C. subtsugae products are heat-killed bacteria and the fermentation media they grew in . The product contains various metabolites and enzymes produced by the bacteria resulting in a broad range of activity mechanisms. It only affects leaf-feeding insects and so is good to use in conjunction with predator mites.

  • Recommended product: Grandevo from Marrone Bioinnovations
  • It does not act as quickly as some other products, and may require 2-3 weekly application before a decline in population is noticed.
  • One study found C. subtsugae to be ineffective on broad mites [36]. It has been demonstrated to be lethal to the two-spotted spider mite but takes multiple days to begin to kill the pests [37].
  • It does not appear to be very effective as a standalone product against russet and broad mites, but can help slow them down and can contibute to a good IPM program for russet mite control because it can be used at lower humidities and in combination with other sprays.
  • A spreader-sticker such as Oroboost should be used with contact insecticides such as Grandevo, Venerate, or pyrethrins.

Marrone Bio Innovations Grandevo WDG Bioinsecticide Miticide OMRI Listed – 6 lbs – 2019 Reformulated

OROBOOST 1 Quart. A Registered Material for use in Organic Agriculture. A Versatile Spreader and penetrant for foliar-Applied miticides, insecticides, fungicides, herbicides and Liquid fertilizers.

Chemical Control


Sulfur is a broad spectrum fungicide, insecticide, and miticide. Because of this, it will kill pests on plant surfaces, but it will also kill beneficial insects and mites. Sulfur can be rough on the epidermis of the plants, and application might chew up the leaves a little bit, but Cannabis can usually handle it well.

  • If you are growing indoors, do not burn elemental sulfur as a control because as it is burned, elemental sulfur becomes sulfur dioxide which can form sulfuric acid with moist leaves, resulting in more severe leaf damage.
  • Sulfur should not be applied in flower, it will persist on the buds and undoubtedly affect the flavor of the buds. However, it can be applied up until flower.
  • Sulfur dust is best applied through a sprayer as a wettable powder. Sulfur should be applied as a wettable powder at about 3 tbsp sulfur/gallon of water. You should test it on a plant before committing to spraying your entire field to make sure that they can handle it.
  • You can also use products such as Safer Brand Garden 3-in-1 spray that contains both sulfur and potassium salts of fatty acids, which also have miticidal activity.
  • I recommend using this as a knock-down if any symptoms are observed and should be followed up with applications of predatory mites and/or fungi. However, I personally would recommend other products as a population knock-down such as pyrethrins where they are allowed.
Bonide (BND1428) – Sulfur Plant Fungicide, Organically Controls Rust, Leaf Spot and Powdery Mildew (4 lb.)

Safer Brand 5452 3-in-1 32-Ounce Ready-to-Use Garden Spray

Safer Brand 3 in1 Garden Spray Concentrate 32 Ounces 5462

Safer Brand 3-in-1 Garden Fungicide 1 Gallon

Neem and Azadirachtin

Azadirachtin is a compound found in neem oil. It is a very good general insecticide and miticide that is found in many IPM programs. It becomes systemic in plants, may act as an antifeedant and may disrupt the maturation process of arthropods that ingest it. In spider mites, it showed a 50% reduction in mites that made it to adulthood [22]. I never recommend using this product in flower because there is some evidence of toxicity and allergy in humans, especially when consumed in large doses [23]. However, this is a very good product to use as a preventative and works well in most IPM programs.

  • Azadirachtin such as AzaMax can be used by itself, as neem oil, or in mixtures. Azera combines azadirachtin with pyrethrins which would be a good knock-down spray to use at first signs of infestation.
  • Ortho tree & shrub fruit tree spray combines neem oil with pyrethrins and piperonyl butoxide. I like to spray neem products at least biweekly during veg to help prevent a broad range of pests including insects, mites, and fungi.

Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil – (16 oz) High Azadirachtin Content – OMRI Listed for Organic Use

Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil 32 oz – OMRI Listed for Organic Use

Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil (1 Gallon) OMRI Listed for Organic Use

AzaMax – 1 Ounce

General Hydroponics GH2045 AzaMax, 4 Ounce

General Hydroponics AzaMax, 16 oz GH2007

AzaMax Quart

AzaMax, Gallon

Azera Gardening 8 oz, Botanical Dual Action Azadirachtin/Pyrethrin Fast-Acting Insecticidal Concentrate for Organic Gardening.

MGK 2905-D30 Azera Insecticide

Ortho Tree & Shrub Fruit Tree Spray, 16-Ounce

Phosphorous Acid

Phosphorous acid, or phosphite, is a very useful tool in the garden. First of all, it is also registered as a fertilizer under different brands and can be used as a foliar spray for feeding phosphorous. It can be in salt form as potassium phosphite which will also provide potassium and may be used as a ‘bloom booster’ in early flower. Recent studies have shown phosphite is not a good fertilizer choice for when phosphate is deficient, however.

  • Phosphorous acid, aside from being a fertilizer, is also a systemic plant resistance activator that helps protect against various fungi including powdery mildew and fusarium.
  • There is a product called MITE-PHITE ZM registered for use in Oregon, but I have not seen wide adoption of this for mite control.
  • At least in the case of spider mites, phosphite may greatly reduce the reproductive rate [24], but it may also be helpful with russet, broad, and cyclamen mites.
  • This is a great general addition to a Cannabis IPM program where approved. I like to spray this at least one time around the time of flipping to flower for both the nutrient content (I use potassium phosphite) and the pest resistance.

Mite Phite is not available on Amazon, but the following products have the same active ingredients (these are registered as fungicides):

Monterey NLG3304, 1 Pint Garden Phos, Brown/A

Organic Laboratories 810-021 Lab QT Organocide Plant Doctor Systemic Fungicde

Quest Reliant Systemic Fungicide (Agri-Fos/Garden Phos) 1 Gallon


Pyrethrins are insecticidal compounds found in the chrysanthemum flower. Please note that pyrethrins are different from pyrethroids. Pyrethrins are extracted directly from the chrysanthemum flower and degrade quickly (within a couple of days) whereas pyrethroids are synthetically produced and are designed to persist for longer periods of time. Pyrethrins are generally a mix of 6 insecticidal compounds. They are neurotoxic to insects but have low toxicity to mammals. Pyrethrins break down fairly quickly on the plant surface. after 5 days, only 3% remains.

  • I recommend buying a pyrethrin product with other additives as well for diversification. However, pyrethrin only products are also effective and may be useful as tank mixes with other insecticides.
    • PyGanic is a great pyrethrin-only product. Finding a product that also contains piperonyl butoxide will improve the effectiveness of the pyrethrins. One such product is Garden Safe Houseplant & Garden Insect Killer
    • For instance, Azera insecticide combines pyrethrins with azadirachtin (another insecticide derived from neem oil)
    • Mighty combines pyrethrins with canola oil. Canola oil is composed mostly of triglycerides which have miticidal activity.
    • Ortho tree & shrub fruit tree spray is a great product that combines pyrethrins, neem oil extract, and piperonyl butoxide. Piperonly butoxide acts to inhibit enzymes that may help insects and mites detoxify the pyrethrins.
    • Safer Brand Pyrethrin & Insecticidal Soap concentrate contains pyrethrins as well as potassium salts of fatty acids.
    • Botanigard Maxx combines pyrethrins with a beneficial fungus, Beauveria bassiana, and this is a great product to use as an initial knockdown that will have some long-lasting effects if the fungi become established in the mite population. Coupled with predatory mite release, this product seems like a good choice.

Garden Safe 80422 Houseplant and Garden Insect Killer 24-Ounce Spray, 2 Pack

PyGanic Gardening 8oz, Botanical Insecticide Pyrethrin Concentrate for Organic Gardening

Insecticide Organic Pyganic 1.4% Pyrethrin 1 Quart Size by Davids Garden Seeds and Products

Azera Gardening 8 oz, Botanical Dual Action Azadirachtin/Pyrethrin Fast-Acting Insecticidal Concentrate for Organic Gardening.

MGK 2905-D30 Azera Insecticide

Mighty is not found on Amazon. Purchase from NPK Industries

NPK Industries Mighty Mite Control (1 qrt)

NPK Industries Mighty Mite Control (1 Gal)

Ortho Tree & Shrub Fruit Tree Spray, 16-Ounce

Safer Brand Insecticidal Soap & Pyrethrin Concentrate, 32-Ounce

Safer Pyrethrin & Insecticidal Soap Concentrate, 1 Gallon

BotaniGard MAXX 32oz. Quart Insect Control Mycoinsecticide

Botanigard Maxx 1 Gallon Beauveria bassiana

Horticultural oils: Mineral Oil, Cottonseed Oil, Soybean Oil, Neem Oil

These oils are hydrophobic liquids that act by suffocating arthropod pests by blocking spiracles. I do not use oils during flower at all because they may affect the flavor or microbial counts on your buds. As I mentioned earlier, I use neem oil during vegetative growth in my IPM program for insects, mites, and powdery mildew issues. Furthermore, if I spray potassium carbonate for powdery mildew control, I also add cottonseed oil if the plant is still in vegetative growth just to add some insecticidal activity to the spray as well. Personally, I recommend sticking to neem oil and cottonseed oil for horticultural oils. Neem oil sprays are also not toxic to P. persimilis, but may be mildly toxic to some Amblyseius species [38, 39]. It is likely the oil itself, not the azadirachtin that is causing issues in Amblyseius, one study found little effect of Azadirachtin on an Amblyseius mite [40]. However, neem oil and mineral oil are both considered compatible with Amblyseius species tested due to a positive population increase [41], but heavy oil applications may slow down population growth.

Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil – (16 oz) High Azadirachtin Content – OMRI Listed for Organic Use

Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil 32 oz – OMRI Listed for Organic Use

Organic Neem Bliss 100% Pure Cold Pressed Neem Seed Oil (1 Gallon) OMRI Listed for Organic Use

Glicks Finest, Pure Cottonseed Oil, 96oz Bottle

Monterey LG 6299 Horticultural Oil Concentrate Insecticide/Pesticide Treatment for Control of Insects, 32 oz

Monterey Horticultural Oil 1gal

Essential Oils

Essential Oils are made by distilling plant materials and collecting volatile compounds that come out of these plants. These are rich in terpenes and other volatile compounds.

  • Garlic oil
  • Rosemary oil
  • Geraniol
  • Rosemary oil
  • Thyme oil

One product, Biomite, was found to significantly reduce spider mite adults and eggs and also did not negatively affect predator mites [42]. Biomite contains Citronella oil, Farnesol, Geraniol, and Nerolidol. This is one of the most cost effective essential oil sprays.

Biomite is not available on Amazon, order from Brandt or Arbico Organics

Some of the best broad spectrum mixtures that contain all approved materials in California include Ed Rosenthal’s Zero Tolerance Herbal Pesticide and Dr. Earth Final Stop Yard & Garden Insect Killer (which also contains a horticultural sesame oil). Bonide mite contains a more insecticidal horticultural oil, cottonseed.

For spider mites, I have heard reports that rosemary oil is the most effective of plant essential oils. For microscopic mites such as broad mites and russet mites, clove oil has been reported as one of the most effective contact killers [personal correspondences].

Dr. Earth Final Stop Cannabis Insect Killer 24oz RTU

Dr. Earth Final Stop Organic Insect Killer 1 gal. – Case of: 4

Bonide (BND285) – Mite-X, Ready to Use Indoor/Outdoor Bug Insecticide and Pesticide (32 oz.),Brown/A

One of my favorite sprays, Lost Coast Plant Therapy, uses a combination of essential oils, horticultural oil, citric acid, and isopropyl alcohol to kill fungi and suffocate/desiccate insects and mites.

Plant Therapy Lost Coast Organic Fungicide, Insecticide, Miticide Natural Plant Protection Concentrate – 12 oz

Lost Coast Plant Therapy 32 oz

Lost Coast Plant Therapy 1 Gallon – Natural Miticide, Fungicide, Insecticide, Kills on Contact Spider Mites, Powdery Mildew

Trifecta crop control is a good product that has a large array of essential oils, corn oil, and citric acid. It is good for contact killing and leaves essential oils that may act as repellants and antifeedants.

Not currently available on Amazon

Citric Acid

Citric acid is a great product to include in any grow. It can act as a fungicide by adjusting leaf pH. It is also a contact miticide and may have over 90% mortality of spider mites [43]. When combined with isopropyl alcohol, it is particularly effective at dessicating mites. However, it is not specific and should not be used with beneficial mites and it does not have activity after the spray.

  • For just citric acid, I recommend using Flying Skull’s product Nuke Em.
  • For mixes of citric acid, isopropyl alcohol, and oils, I recommend either Green Cleaner (Central Coast Garden Products) or Plant Therapy (Lost Coast).
  • Trifecta crop control uses citric acid in conjunction with essential oils, corn oil, and soap.

Plant Therapy Lost Coast Organic Fungicide, Insecticide, Miticide Natural Plant Protection Concentrate – 12 oz

Lost Coast Plant Therapy LCPT0032, 32 oz, Case of 12 Nutrients, Blue, Green

Lost Coast Plant Therapy 1 Gallon – Natural Miticide, Fungicide, Insecticide, Kills on Contact Spider Mites, Powdery Mildew

Green Cleaner 749804 Sprayer Home Pest Control, 8 oz

Green Cleaner CCGC1032, 32 oz, Home Pest Concentrate, 1 Quart, Liquid

Central Coast Garden Products CCGC1128 Green Cleaner 749808 Plant Wash, 1 Gallon

FLYING SKULL CUSTOS PLANTAM PLANT PRODUCTS Nuke em Insecticide & Fungicide, 8 oz

FLYING SKULL CUSTOS PLANTAM PLANT PRODUCTS Nuke em Insecticide & Fungicide, 1 Quart

FLYING SKULL CUSTOS PLANTAM PLANT PRODUCTS Nuke em Insecticide & Fungicide, 1 Gallon

Insecticidal Soaps (Potassium Salts of Fatty Acids)

Insecticidal soaps work by disrupting cell membranes and disrupting cuticles. They kill on contact and degrade rapidly. They do not leave an insecticidally active residue after drying. Therefore, I would not rely on this as your main control method. It may be useful for an initial knockdown or in conjunction with other chemicals. Frequent insecticidal soap applications can be effective for control of spider mites [44]. Personally, I don’t like using insecticidal soap in flower.

  • Any brand will work fine; I recommend Safer Brand insecticidal soap 3 in 1 because it also contains sulfur which increases the efficacy and protects the plant for longer, or Safer Brand Pyrethrin & Insecticidal Soap concentrate.

Safer Brand 3 in1 Garden Spray Concentrate 32 Ounces 5462

Safer Brand 5118-6 Insect Killing Soap Concentrate 16oz

Safer Brand Insecticidal Soap & Pyrethrin Concentrate, 32-Ounce

Example IPM Program:

Simple, Cheap, Preventative:

  1. Veg: Weekly application of neem oil product or sulfur product or essential oil product. If using neem or essential oils, can be combined with predatory mite release. Azadirachtin products may also replace neem oil or be mixed with neem/essential oils.
  2. Flower: Weekly application of citric acid product such as Nuke Em or Plant Therapy or monthly release of predatory mites

More Complex

  1. Veg: Weekly application of neem oil or essential oil product (such as Trifecta or Zero Tolerance). These may be rotated on a biweekly basis and may be mixed with an azadirachtin product such as Azamax.
    1. Monthly release of predatory mites
    2. You can include a citric acid product in rotation, but only before mite release and it must be allowed to dry. You can increase time in between neem oil sprays under low pressure up to 14 days.
      1. Day 1: spray citric acid product such as plant therapy
      2. Day 2: release predatory mites
      3. Day 8: Spray Neem or essential oils (avoid purified azadirachtin)
      4. Day 15: Spray neem/essential oils or phosphorous acid
      5. Day 22: Spray neem/essential oils
      6. Day 29: Spray citric acid product
      7. Day 30: Release predatory mites
  2. Flip to Flower: Potassium salts of phosphorous acid spray
  3. Flower: Weekly application citric acid product such as Plant Therapy or Nuke Em or rotation of citric acid product and phosphorous acid product.
    1. Example of using predators, citric acid, and phosphorous acid:
      1. Day 1: spray citric acid product. Allow to dry.
      2. Day 2: release predatory mites
      3. Day 15: Spray phosphorous acid product (time between application may be decreased to 7-10 days if pressure is high)
      4. Day 29: spray citric acid product. Allow to dry.
      5. Day 30: Release predatory mites

The following program is aggressive for if an infestation occurs. It requires a diverse range of products but will be highly effective assuming proper environmental conditions for biologicals:

Day 1: Citric acid product knockdown (optional but recommended)

Nuke Em: citric acid, also contains insecticidal soap

Plant Therapy: citric acid, isopropyl alcohol, oils

Day 2 or 3 (when dry) second knockdown: Veg options: All are good choices

  • Azera (pyrethrins+azadirachtin)
  • Mighty (pyrethrins+ canola oil)
  • Ortho tree & shrub fruit tree spray (pyrethrins+neem oil+piperonyl butoxide)
  • Garden safe 3-in-1 (sulfur+insecticidal soaps)
  • Safer brand pyrethrins & insecticidal soap concentrate
  • Pyganic gardening (pyrethrins)
  • Bonide tomato and vegetable conc. (sulfur+pyrethrins)
  • Sulfur may be tank mixed with pyrethrins & insecticidal soaps,
  • Botanigard Maxx (Pyrethrins & B. bassiana)

Flower Options– Only use pyrethrins if you are still early in flowering. Otherwise, it is best to stick to food grade contact killer such as citric acid.

  • Safer brand pyrethrins & insecticidal soap concentrate
  • Pyganic gardening (pyrethrins)
  • Botanigard Maxx

Day 5 or 6: Second pyrethrin application, begin biological control with B. bassiana or I. fumosorosea and mites

  • Botanigard Maxx
  • Pyganic + Botanigard/Mycotrol
  • Pyganic+ PFR-97

Day 6 or 7: Release predator mites when previous spray is dry

Day 10: Grandevo or Venerate spray

Day 15: PFR-97 or Mycotrol/Botanigard spray (diversifying from last living fungus spray is recommended, but requires multiple products).

Assuming the infestation is severe, I would rotate between day 1 and day 2 applications for a longer period of time (1-2 weeks) before implementing more persistent biological control methods.

*If ambient humidity is low (<40% RH), I would rotate between Grandevo, Venerate, and Citric Acid (Nuke Em or Plant Therapy) instead of using living fungi*

Day 20: Grandevo or Venerate spray (Diversifying from last heat-killed bacteria is recommended)

Day 27: PFR-97 or Mycotrol/Botanigard

Day 35: Grandevo or Venerate

Day 36: Release predatory mites

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  37. Grandevo In Action: Twospotted Spider Mite | Marrone Bio Innovations. (n.d.). Retrieved April 9, 2020, from https://marronebio.com/grandevo-action-twospotted-spider-mite/
  38. Duchovskienė, L., Raudonis, L., Karklelienė, R., & Starkutė, R. (n.d.). Toxicity of insecticides to predatory mite Phytoseuilus persimilis in cucumber.
  39. Koul, O. (2004). Neem: Today and in the New Millennium. https://doi.org/10.1007/1-4020-2596-3
  40. Castagnoli, M., Angeli, G., Liguori, M., Forti, D., & Simoni, S. (2002). Side effects of botanical insecticides on predatory mite Amblyseius andersoni (Chant). Anzeiger Für Schädlingskunde, 75, 122–127. https://doi.org/10.1046/j.1472-8206.2002.02035.x
  41. ROCHA DA SILVA, R., VIEIRA TEODORO, A., De Sousa Silva, M. D. J., REBELLES REIS, P., & SANTOS SILVA, S. (2015). Compatibility of pesticides with the generalist predatory mite Amblyseius largoensis (Acari: Phytoseiidae). Revista Colombiana de Entomología, 41(1), 76–80.
  42. Development and Implementation of Sustainable Biologically-Based Pest Management Systems for High Value Specialty Crops in Central Washington – WASHINGTON STATE UNIVERSITY. (n.d.). Retrieved April 9, 2020, from https://reeis.usda.gov/web/crisprojectpages/0189651-development-and-implementation-of-sustainable-biologically-based-pest-management-systems-for-high-value-specialty-crops-in-central-washington.html
  43. Cloyd, R. A., Galle, C. L., Keith, S. R., Kalscheur, N. A., & Kemp, K. E. (2009). Effect of Commercially Available Plant-Derived Essential Oil Products on Arthropod Pests. Journal of Economic Entomology, 102(4), 1567–1579. https://doi.org/10.1603/029.102.0422
  44. Osborne, L. S. (1984). Soap Spray: An Alternative to a Conventional Acaricide for Controlling the Twospotted Spider Mite (Acari: Tetranychidae) in Greenhouses. Journal of Economic Entomology, 77(3), 734–737. https://doi.org/10.1093/jee/77.3.734
  45. Pyrethrins: General Fact Sheet. (n.d.). Retrieved April 10, 2020, from http://npic.orst.edu/factsheets/pyrethrins.pdf
  46. JACOBSON, R. J., CHANDLER, D., FENLON, J. & RUSSELL, K. M. (2001). Compatibility of Beauveria bassiana (Balsamo) Vuillemin with Amblyseius cucumeris Oudemans (Acarina: Phytoseiidae) to control Frankliniella occidentalis Pergande (Thysanoptera:Thripidae) on cucumber plants. Biocontrol Science and Technology11, 381 – 400.
  47. Midthassel, A., Leather, S., Wright, D., & Baxter, I. (2016). Compatibility of Amblyseius swirskii with Beauveria bassiana: two potentially complimentary biocontrol agents. BioControl, 61. https://doi.org/10.1007/s10526-016-9718-3

Fusarium Wilt and Fusarium Bud Rot in Cannabis (Hemp and Marijuana)

Anyone involved in plant pathology can tell you that the genus Fusarium is one of the most damaging group of fungi to crops. There are many species of Fusarium that cause disease on different crops. Some infections can cause devastating root rots and vascular diseases, some can cause cankers on branches and stems, and some can even infect foliage. Yield losses can be dramatic in some circumstances. For instance, in 1999 in northern Great Plains and central USA, Fusarium head blight of winter wheat alone suffered $2.7 billion losses [32]. In tomato, when disease is severe, crop losses can reach 80% [33].

In Cannabis, two formae speciales of F. oxysporum have been described as causing Fusarium wilt: Fusarium oxysporum f. sp. vasinfectum (FOV) and Fusarium oxysporum f. sp. cannabis (FOC) [2, 21]. Furthermore, Fusarium solani has been found to be prevalent in hydroponic Cannabis grown in Canada [21]. Furthermore, F. brachygibbosum and F. equiseti have been isolated (in addition to F. oxysporum and F. solani) from symptomatic field-grown Cannabis plants in Northern CA [23]. F. oxysporum has been isolated from wilted Cannabis plants that does not match with either of the formae speciales cannabis or vasinfectum [21].

Fusarium oxysporum species complex

Fusarium oxysporum is a diverse species; some species are harmless soil inhabitants, while some are plant pathogens. Arguments have been presented that there may be at least two phylogenetically distinct species based on DNA sequencing, and that most plant pathogens belong two one of these groups (PS2) [1].

Forma specialis is not a phylogenetically recognized categorization; it is a way for plant pathologists to discuss particular isolates of Fusarium species that attack particular plant species. A forma specialis is generally named after the diseased plant that it was isolated from, this is why one of the isolate groups that infect Cannabis is called F. oxysporum f. sp. cannabis. The two formae speciales that infect Cannabis can be distinguished by their host range. FOC only infects Cannabis, whereas FOV has a wider host range and can infect cotton, coffee, and other plants. F. oxysporum has at least 100 different species-specific isolates. Sexual reproduction has not been observed in this species, but horizontal gene transfer likely had an important role in the evolution of this organism [1]. all observed spores from F. oxysporum are asexual in nature.

Infections begin with the germination of spores or growth of mycelium into plant roots through injured areas or sites of lateral root emergence. The filamentous mycelium penetrates into the xylem vessels and begins colonizing the plant’s vasculature. It becomes systemic and can form sporulating structures known as sporodochia on aerial parts of the plant. The sporodochia produce conidia (2 types, microconidia and macroconidia [macroconidia is larger, multinucleate, and multiseptate]). The conidia is carried by wind and air. When it comes to overwintering, Fusarium can survive in the infected crop residues, but it can also make overwintering asexual spores known as chlamydospores. Chlamydospores don’t require special structures to form, they can form at the terminal ends of fungal hyphae or within the hyphae (intercalary). They are generally thick walled, melanized, and multicellular spores.

Image from Plant Pathology 5th Edition, Agrios (2005)

This disease of Cannabis has been amplified through human activity. Fusarium oxysporum is a deadly pathogen and it has been foolishly used as a mycoherbicide all over the world in order to try to kill ‘illicit’ Cannabis plants [2, 3]. All cultivars that have been tested are susceptible to the disease. In native ecosystems, F. oxysporum is not known to be a major disease risk. It seems that through intensive agriculture and monocropping, more pathogenic and virulent isolates have been able to evolve and amplify their populations clonally [1].

Fusarium solani species complex [22]

F. solani, much like F. oxysporum, was previously divided into formae speciales based on the host range. However, recent phylogenetic studies have determined that different formae speciales are really unique species, and the F. solani species complex (FSSC) is divided into at least 60 unique species. Some of these species have been renamed, but many are still unnamed and are referred to by ‘haplotype number’, which is basically just a number that represents certain genotypes. The FSSC has a wide host range, and even particular species within the FSSC can have broad host ranges. Unlike in the FOSC, sexual reproduction has been observed in some species in the FSSC.

The life cycles, infection techniques, and symptoms are very similar between FOSC and FSSC, so I when I mention Fusarium from here on out, I will be referring to all Fusarium sepecies capable of causing root rots of Cannabis.

Root Infection

Chlamydospores require a conducive environment to germinate and cause disease. In soil, this generally means the presence of root exudates [34]. Because of this, only spores in very close proximity to roots actually pose a disease risk. The rhizosphere (which I will define as the area of soil directly affected by the root exudates) is generally very small (<1 mm) from the plant root [9, 10]. The actual volume of soil that falls within this distance from roots is typically under 35%, even for plants with extensive roots and highly active exudation [1]. However, evidence of targeted growth of germinated spores towards roots is lacking (i.e. lacking evidence for chemotaxis) [11]. Infections may fail to establish, especially in the case of a rapidly growing root (spore germinates in response to root exudate, if the germ tube reaches the root, chances are the root tip has already advanced and the fungus is now encountering more differentiated plant tissue more capable of defensive responses) [12].

Flower and Seedling Infection

Along with Pythium, Fusarium can cause damping off of seedlings. Infection can begin in roots or the hypocotyl and can quickly invade the vasculature [21].

Fusarium usually begins its infection cycle from chlamydospores in the soil. However, as the infection progresses, sporodochia form on the crown and lower stem that produce conidia. Conidia can become airborne and can infect aerial portions of the plant. In particular, it can readily form flower infections and cause bud rot. Flower-infecting species include F. solaniF. oxysporum and F. equiseti [25]. F. solani appears to be the most aggressive species. It appears that the F. oxysporum that has been isolated from flowers is the same type involved in root infections [25]. These Fusarium species can directly infect the bracts and pistils of flowers.

In hydroponics, Fusarium can be particularly aggressive [13]. In fact, researches generally use aqueous spore suspensions in experiments to guarantee that the plant is inoculated. First of all, the spores are essentially in suspension and circulate around the water, almost guaranteeing that the spores will come in direct contact with the roots. Furthermore, the spores can directly adhere to the root tips, foregoing the need for germ tubes to find their way through soil to the plant roots and decreasing the chance that the plant root can grow faster than it takes for the fungal mycelium to reach the root. This allows easy access for the fungus to susceptible meristematic tissue. Root tip infection does not occur for all plant species, but spore adhesion to roots certainly does raise disease risk for any plant species.

Once the fungal mycelium contacts a root, the fungus proliferates into a hyphal network to maximize points of contact. They likely utilize cell wall degrading enzymes to form an opening, and the mycelium can then penetrate directly through epidermal cells or may grow in between cells [1]. Either way, growth advances towards the root cortex.

Necrotroph or Biotroph?

For those who have read my articles on two other major Cannabis pathogens, bud rot and powdery mildew, you may be aware that pathogenic fungi can have a variety of different strategies. A biotroph requires the host cells to be alive and extracts nutrients from the living host cells (a true parasite, such as PM [manipulates host immune responses]), whereas a necrotroph such as the bud rot pathogen Botrytis cinerea induces or causes cell death to overcome plant resistance responses and have dead organic matter to feed on (it may be argued that there is a brief biotrophic phase in bud rot but in general can be viewed as a necrotroph).

Strictly speaking, Fusarium is necrotrophic because even isolates that do not cause any visible damage to a given plant (nonpathogenic) are observed to grow intracellularly and cause cell death on a microscopic level [14]. However, as mentioned, there are many cases of F. oxysporum isolates not causing any really visible disease or crop losses, or even examples of isolates that cause disease symptoms on some plant species but can colonize the roots of other plant species without causing visible disease symptoms. In these cases, though necrotrophy is visible on a microscopic level, F. oxysporum may be considered an endophyte, and the complexity of the relationship between endophytic Fusarium isolates and their plant hosts are not fully understood [1, 15, 16, 17, 18]. In fact, F. oxysporum can even be isolated as an endophyte from nonsymptomatic Cannabis plants [24].

There have been some conflicting reports as to how the wilt disease progresses (this will mostly focus on studies done with F. oxysporum in flax), but the differences might be attributable to environmental differences between studies, differences in how microscopic images were interpreted, or it may even be evidence that different isolates within a given forma specialis may span a spectrum of necrotrophic and biotrophic lifestyles.

Disease Cycle Proposition 1: The extended biotrophic phase [19]

  1. The fungus has an extended biotrophic phase in which infected cells remain viable and the fungus can continually be isolated from seemingly disease-free root tips.
  2. After entering the xylem vessels, the fungus grows in the vessels and feeds on the nutrients carried within the xylem. It continues to grow until the vessels become occluded (blocked), either through the accumulation of fungal biomass or through plant responses such as forming tyloses.
  3. After xylem occlusion and plant wilting/death, the fungus then grows out of the vasculature and begins a necrotrophic phase in which is begins killing and feeding on all other plant tissues.

Disease cycle proposition 2: The true necrotroph [20]

  1. No biotrophic phase observed, cell death is common among all cells the fungus comes in contact with.
  2. Infection of roots leads to root cell death and necrosis before the fungus even reaches xylem vessels (i.e. root rot can precede systemic vascular infection)
  3. Fungus aggressively colonizes both vasculature and other tissues


  • Initial symptoms can look similar to Nitrogen deficiencies. Chlorosis of lower leaves and slight wilting becomes evident. Plant stunting is common, especially in the case of F. solani infection
Left plant is uninoculated. Middle plant inoculated with F. oxysporum, right plant inoculated with F. solani.
Image adapted from Punja, Z., Scott, C., & Chen, S. (2018). Root and crown rot pathogens causing wilt symptoms on field-grown marijuana ( Cannabis sativa L.) plants.
  • The crown region of the plants become darkly discolored and sunken. Discoloration of the vasculature can extend up to 15cm from the soil surface.
Image adapted from Punja, Z., Scott, C., & Chen, S. (2018). Root and crown rot pathogens causing wilt symptoms on field-grown marijuana ( Cannabis sativa L.) plants.
Showing discolored pith. Image adapted from Image adapted from Punja et al. (2019). Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.
  • In hydroponics, roots become discolored
Image adapted from Punja, Z. K., Collyer, D., Scott, C., Lung, S., Holmes, J., & Sutton, D. (2019). Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.
  • When xylem vessels become occluded, whole plants can begin to wilt.
Image adapted from Punja, Z. K., Collyer, D., Scott, C., Lung, S., Holmes, J., & Sutton, D. (2019). Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.
  • In this hydroponic system, the Fusarium wilt ended up killing the plant.
Image adapted from Punja, Z. K., Collyer, D., Scott, C., Lung, S., Holmes, J., & Sutton, D. (2019). Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.
  • Sporodochia form on the necrotic stem and the spores can become airborne, infecting surrounding plants. In humid conditions, mycelium can grow out of the stem
Image adapted from Punja, Z. K., Collyer, D., Scott, C., Lung, S., Holmes, J., & Sutton, D. (2019). Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.
  • Fusarium can cause damping off in seedlings and clones as seen in the following tray of clones:
Image adapted from Punja, Z. K., Collyer, D., Scott, C., Lung, S., Holmes, J., & Sutton, D. (2019). Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.
  • Fusarium oxysporum can cause bud rot! When inoculated on flowers, they can cause necrosis of the buds very similar to Botrytis cinerea. The mycelium is usually much more white than the mycelium from B. cinerea.
Image adapted from Punja, Z. K., Collyer, D., Scott, C., Lung, S., Holmes, J., & Sutton, D. (2019). Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.
The Effect Of Fusarium On Marijuana Plants - Grasscity Magazine ...
Image from https://growersnetwork.org/cultivation-resources/growers-networks-disease-profile-fusarium-wilt/
  • Depending on where the infection occurs, wilting can be evident on some branches/colas but not others.
Image from https://www.lahuertagrowshop.com/blog/como-prevenir-y-eliminar-fusarium-en-plantas-de-marihuana/


What Factors Favor Fusarium Development?

For F. oxysporum f. sp. lycopersici (the forma specialis that infects tomato), the following factors favor wilt development (28):

  • Soil and air temperatures of 28°C (Too warm (34°C) or too cool (17-20°C) will inhibit development)
  • Low nitrogen and phosphorus, high potassium
  • Low soil pH
  • Short day day length
  • Low light
  • use of ammonium nitrogen

Root exudates appear to stimulate spore germination and drive plant infection. However, certain techniques based on manipulating the soil microbiome may be beneficial in controlling the severity of Fusarium wilt.

  • Amending soil with organic matter to promote microbial activity may make soils more disease-resistant [4].
  • Soil treatments aimed at reducing the number of viable fungal propagules in the soil such as anaerobic soil disinfestation (ASD) [5] and solarization [6].
    • ASD is a process of flooding a field and covering with a plastic ‘mulch’. Anaerobic bacteria multiply and gasses from these bacteria accumulate under the plastic mulch.
    • Solarization is the process of putting a black plastic over a field during hot seasons in direct sun to raise soil temperatures.
  • Certain bacteria or microbial groups may contribute to how conducive a soil is to disease development
    • For instance, a species of Arthrobacter in suppressive soils was associated with greater levels of lysis of fungal germ tubes from soil chlamydospores [7].
      • Soils that are more disease suppressive are sometimes associated with certain microbial groups in the soil microbiome [8]

Resistant Cultivars

Resistant strains undoubdtedly can be bred for. In hemp, SF and CF cultivars appear to be more resistant than the cultivar Iran [3]. I am not sure what strains are best in regards to marijuana cultivars with resistance to Fusarium, and I am struggling to find information on this. Comments with relevant information on this would be appreciated.

Biocontrol Agents

I will list some approved spray/soil drench control methods, but can not promise the effectiveness of any method, much cannot be found in literature.

  • In Canada, possible biocontrol agents for Fusarium infections in foliage and flowers include Prestop WP (Gliocladium catenulatum strain J1446) and Rootshield WP (Trichoderma harzianum Rifai strain RRL-AG2) [25].
    • These microbes will be counted on CFU testing, so should not be applied late in locations that test using this method.
  • In Canada, approved biocontrol agents for root-infecting pathogens are Rootshield WP (Trichoderma harzianum Rifai strain RRL-AG2) and Prestop WP (Gliocladium catenulatum strain J1446) [21].
  • In California, Gliocladium virens, Trichoderma harzianum, and Bacillus amyloliquefaciens strain D747 are approved biofungicides [26].
  • Other possible biocontrol biocontrol agents include Rhapsody (Bacillus subtilis strain QST 713) and Mycostop (Streptomyces griseoviridis strain K61) [21].

Plant Activators

In California extract of Giant Knotweed (Reynoutria sachalinensis) REGALIA® Rx Biofungicide is an approved fungicide.

Marrone Bio Innovations Regalia Biofungicide Fungicide inhibits fungal and Bacterial Disease Boosting Yield, 0-Day PHI, 4 Hour REI, OMRI Listed (1 Gallon)

Kelp extracts (contain arachadonic acid) and crab meal/insect frass (contain chitin) may be useful soil amendments for priming plant resistance to soil borne fungal pathogens.

Liquid Kelp Extract Seaweed 32 Ounce Fertilizer Concentrate

In Oregon, potassium phosphite such as Agri-Fos, (which happens to also be a good source of potassium and phosphorus in flower) is also approved as a plant protectant and fungicide

Monterey Agri-Fos Disease Control Fungicide – Pint LG3340

Quest Reliant Systemic Fungicide (Agri-Fos/Garden Phos) 1 Gallon

Cultural Methods

  • Control and prevention should include efforts to reduce inoculum loads. For growers using hydroponics (including coco) and/or indoor grows: ultraviolet light in ducting and even the grow area (which also may increase cannabinoid production if used correctly), ozonation of the grow area (too high of a level may have negative effects on plant and human health), chlorination of water used in hydroponics, hydrogen peroxide flushes of the root zone (or products such as Zerotol which also contains peroxyacetic acid), heat pasteurization and/or mechanical filtration of water [21].DPD ZeroTol 2.0 2.5GAL
  • It is a good idea to remove wilted plants to prevent aerial spore transfer and quickly remove any infected flowers or branches, especially in environments of high humidity.
  • In hydroponics, keeping nutrient solution at temperatures between 17℃ and 22℃ is ideal for preventing pathogens, promoting water oxygenation, and preventing growth retardation of the plants. Active Aqua AACH10HP Water Chiller Cooling System, 1/10 HP, Rated per hour: 1,020 BTU, User-Friendly
  • Always sterilize your tools in between cuts, wear proper PPE to avoid introducing inoculum.
  • Despite common conceptions that Fusarium grows best in flooded soils, many Fusarium species actually grow best in aerobic, well-draining soil [30]. Another study similarly found F. oxysporum f. sp. lycopersici to not grow in saturated soils. However, plants were actually resistant to infection at soil moisture contents of 13%-19% [31].
    • In short, it is good to let your soil dry between waterings (not to the point of plant wilting though). Fusarium grows best in aerobic (well-draining), and moist but not flooded soils (i.e. most coir or peat based media).
    • Anaerobic soil disinfestation (ASD) may be a good way to reduce soil inoculum levels between grows in no-till systems.

Foliar/Flower Controls

The most important factor in preventing flower infections from Fusarium is probably humidity [25]. Flower infection relies on airborne conidia released from the sporodochia (spore-bearing structures) on aerial tissue of the plant. Humidity needs to be high in order to successfully form these sporodochia. A different Fusarium species, F. graminearum requires humidity of over 85% RH to form perithecia (sexual spore-bearing structure of this species) [27].

For Fusarium oxysporum f. sp. erythroxyli (this paper is unfortunately discussing the possible use of this Fusarium species to kill the ‘illicit narcotic’ coca plant), the isolate was found to sporulate at relative humidities (RHs) between 75% and 100% [29]. Fusarium‘s primary route of infection is through the roots in soil, and it is a bit easier to control for aerial infections than soil infections in Cannabis.

General humidity control aiming to correlate with vapor pressure deficit conditions or slightly lower for IPM reasons (around 60% RH in veg, 50% in flower down to 40% the last couple weeks of flower) should be good enough to prevent a lot of aerial sporulation. Good airflow and ciculation is definitely recommended to reduce high-humidity microclimates.

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  2. McPartland, J. M., & Hillig, K. W. (2004). CANNABIS CLINIC Fusarium Wilt. Journal of Industrial Hemp, 9(2), 67–77. https://doi.org/10.1300/J237v09n02_07
  3. Council, N. R. (2011). Feasibility of Using Mycoherbicides for Controlling Illicit Drug Crops. The National Academies Press. https://doi.org/10.17226/13278
  4. Bonanomi G, Antignani V, Capodilupo M, Scala F. 2010. Identifying the characteristics of organic soil amendments that suppress soilborne plant diseases. Soil Biol. Biochem. 42:136–44
  5. Hewavitharana SS, Mazzola M. 2016. Carbon source–dependent effects of anaerobic soil disinfestation on soil microbiome and suppression of Rhizoctonia solani AG-5 and Pratylenchus penetrans. Phytopathology 106:1015–28
  6. Greenberger A, Yogev A, Katan J. 1987. Induced suppressiveness in solarized soils. Phytopathology 77:1663–67
  7. Smith SN. 1977. Comparison of germination of pathogenic Fusarium oxysporum chlamydospores in host rhizosphere soils conducive and suppressive to wilts. Phytopathology 67:502–10
  8. Mazzola M. 2004. Assessment and management of soil microbial community structure for disease suppression. Annu. Rev. Phytopathol. 42:35–59
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  10. Rovira AD. 1969. Plant root exudates. Bot. Rev. 35:35–57
  11. Olivain C, Humbert C, Nahalkova J, Fatehi J, L’Haridon F, et al. 2006. Colonization of tomato root by pathogenic and nonpathogenic Fusarium oxysporum strains inoculated together and separately into the soil. Appl. Environ. Microbiol. 72(2):1523–31
  12. Beckman CH. 1987. The Nature of Wilt Diseases of Plants. St. Paul, MN: Am. Phytopathol. Soc. 175 pp
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  18. Scott JC, McRoberts DN, Gordon TR. 2014. Colonization of lettuce cultivars and rotation crops by Fusarium oxysporum f. sp. lactucae, the cause of Fusarium wilt of lettuce. Plant Pathol. 63:548–53
  19. Turlier M-F, Eparvier A, Alabouvette C. 1994. Early dynamic interactions between Fusarium oxysporum f. sp. lini and the roots of Linum usitatissimum as revealed by transgenic GUS-marked hyphae. Can. J. Bot. 72:1605–12
  20. Kroes GMLW, Baayen RP, Lange W. 1998. Histology of root rot of flax seedlings (Linum usitatissimum) infected by Fusarium oxysporum f. sp. lini. Eur. J. Plant Pathol. 104:725–36
  21. Punja, Z. K., & Rodriguez, G. (2018). Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology, 40(4), 498–513. https://doi.org/10.1080/07060661.2018.1535466
  22. Coleman, J. J. (2016). The Fusarium solani species complex: ubiquitous pathogens of agricultural importance. Molecular Plant Pathology, 17(2), 146–158. https://doi.org/10.1111/mpp.12289
  23. Punja, Z., Scott, C., & Chen, S. (2018). Root and crown rot pathogens causing wilt symptoms on field-grown marijuana ( Cannabis sativa L.) plants. Canadian Journal of Plant Pathology, 40. https://doi.org/10.1080/07060661.2018.1535470
  24. Punja, Z. K., Collyer, D., Scott, C., Lung, S., Holmes, J., & Sutton, D. (2019). Pathogens and Molds Affecting Production and Quality of Cannabis sativa L. Frontiers in Plant Science, 10, 1120. https://doi.org/10.3389/fpls.2019.01120
  25. Punja, Z. K. (2018). Flower and foliage-infecting pathogens of marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology, 40(4), 514–527. https://doi.org/10.1080/07060661.2018.1535467
  26. Department of Pesticide Regulation, C. (n.d.). CANNABIS PESTICIDES THAT ARE LEGAL TO USE. Retrieved March 28, 2020, from http://www.cdpr.ca.gov/cannabis
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  28. Fusarium oxysporum f. sp. lycopersici. (n.d.). Retrieved March 28, 2020, from https://projects.ncsu.edu/cals/course/pp728/Fusarium/Fusarium_oxysporum.htm
  29. Gracia-Garza, J. A., & Fravel, D. R. (1998). Effect of Relative Humidity on Sporulation of Fusarium oxysporum in Various Formulations and Effect of Water on Spore Movement Through Soil. PhytopathologyTM, 88(6), 544–549. https://doi.org/10.1094/PHYTO.1998.88.6.544
  30. Stover, R. H. (1953). THE EFFECT OF SOIL MOISTURE ON FUSARIUM SPECIES. Canadian Journal of Botany, 31(5), 693–697. https://doi.org/10.1139/b53-050
  31. Clayton, E. (1923). The Relation of Soil Moisture to the Fusarium Wilt of the Tomato. American Journal of Botany, 10(3), 133-147. Retrieved March 29, 2020, from http://www.jstor.org/stable/2435361
  32. Goswami, R. S., & Kistler, H. C. (2004). Heading for disaster: Fusarium graminearum on cereal crops. Molecular Plant Pathology, 5(6), 515–525. https://doi.org/10.1111/j.1364-3703.2004.00252.x
  33. Fusarium Wilt in Processing Tomatoes – Seminis. (n.d.). Retrieved March 29, 2020, from https://seminis-us.com/resources/agronomic-spotlights/fusarium-wilt-in-processing-tomatoes/
  34. Akhter, A., Hage-Ahmed, K., Soja, G., & Steinkellner, S. (2016). Potential of Fusarium wilt-inducing chlamydospores, in vitro behaviour in root exudates and physiology of tomato in biochar and compost amended soil. Plant and Soil, 406(1), 425–440. https://doi.org/10.1007/s11104-016-2948-4

Disease Profile: Powdery Mildew of Cannabis

Powdery mildew is usually first observed as small white circular spots on Cannabis leaves. They can be faint, but they begin to cover entire leaves if left unchecked and can begin to grow on buds as well.

White powdery mold growing on cannabi leaves like spots of flour
Photo taken from White Powdery Mildew on Cannabis Plants – Identification & Solution! (n.d.). Retrieved February 12, 2020, from https://www.growweedeasy.com/cannabis-plant-problems/white-powdery-mildew

Photo taken from Is Powdery Mildew Systemic? | Medicinal Genomics. (n.d.). Retrieved February 12, 2020, from https://www.medicinalgenomics.com/powdery-mildew-systemic/


For powdery mildew, the conditions that favor the host, also favor the pathogen. Dry leaves, warm temperatures, and moderate to high humidity. It can tolerate low humidity as well

Many websites out there will tell you that powdery mildew in Cannabis prefers cool temperatures and low humidity. Powdery mildew can be one of the most difficult diseases to control because it grows best in the same conditions as your Cannbis plants. However, PM can tolerate a wide range of RH levels, and simply lowering your RH levels will not eliminate PM risk, though it does help. In fact, low humidity can favor the spread of the disease, but high humidity can favor spore germination (although liquid water in contact with spores will inhibit germination).

Powdery Mildew on Cannabis: The Summary

What PM Species Affect Cannabis? What Environmental Conditions help control PM on Cannabis?

Much of the information on popular websites for Cannabis Powdery Mildew conflicts with the information in the scientific literature. I will report what has been published in scientific literature. Powdery mildew fungi often have a narrow host range. They are known as biotrophs, meaning that they can only live and reproduce on living hosts. Coincidentally, they also cannot be cultured in vitro because they require the living host to survive. There is a closer evolutionary relationship between the host and the parasitic fungus than that of necrotrophic fungi such as B cineria, the causal agent of bud rot.

Many species have historically been identified as capable of infecting Cannabis. In the early 1990s, McPartland reported at least 2 different species (Leveillula taurica and Sphaerotheca macularis) [1i, 2i]. In 2018, a Canadian publication described the causal agent of Cannabis Powdery Mildew in samples from drug Cannabis as belonging to the Golovinomyces cichoracearum species complex from looking at ITS sequences, which may include other species such as G. spadiceus or G. ambrosiae [1]. Subsequent studies show that G. spadecius is a common PM pathogen on Cannabis species [2, 3,]. Cannabis can also be infected by PM from closely related plant species such as hop PM, Podosphaera macularis [2].

Golovinomyces spadiceus grows best in warm, low humidity climates. It is commonly found on wild plant species such as wild sunflower [4] or plants within the same tribe, such as Zinnia flowers and various other plants [5, 6]. Cannabis can get a decent amount of infection on the flowers, and this can lead to unmarketability in the private and medical sectors. It is not recommended to consume bud infected with PM, though I do not believe there is any research as to the health effects of consuming Cannabis infected with PM. It can certainly destroy trichomes and affect the flavor and odor of your buds is you have a heavy infection.

When temperatures drop, the relative humidity of your grow area will go up because cooler air holds less water and condenses water easily [7]. The tomato-infecting PM species, which has also been reported as infecting Cannabis, is signifiantly reduced at low humidity levels (20-40% RH) [8], and this is a common recommendation for Cannabis growers. For G. spadiceus, the pathogen is presumed to act similarly, and keeping humidity under 50%, and preferably lower is ideal for controlling Powdery Mildew. For instance, one report of G. spadiceus in Cannabis says that G. spadiceus thrives in warm temperatures and moderate to high humidity [9].

The Biology of Powdery Mildew

Powdery mildew are ascomycete fungi in the order Erysiphales. As mentioned, they are obligate biotrophs. The life cycle of PM is shown below. This diagram is for grape powdery mildew, though the life cycle is the same for PM on most plants

Powdery Mildew of Grape | Ohioline. (n.d.). Retrieved February 15, 2020, from https://ohioline.osu.edu/factsheet/plpath-fru-37

Cleistothecia are structures produced in the late summer that are known as ‘overwintering structures’, meaning they help protect the sexual spores (ascospores) inside until they are released in the Spring. They are far more resilient than the conidia spores that are asexually reproduced in the disease’s main reproduction cycle that provides secondary infections during the Spring, Summer, and Fall. Ascospores are sexually produced spores, meaning that they undergo sexual recombination, whereas conidial spores have the same genotype as the isolates that formed them. Conidia begin to be produced quickly, usually within a week of initial infection, leading to rapid disease spread and exponential growth of the pathogen.

PM fungi, despite what some Cannabis websites claim, are not systemic. For a pathogen to be systemic, is has to be able to spread via the vasculature of plants. Of course, it can spread to distant parts of the plant through spread of spores or growth of mycelium over susceptible tissue. I would hypothesize that websites that claim that asymptomatic tissues are testing positive despite showing symptoms are simply identifying spores or initial infections that are not yet visible to the naked eye.

PM fungi only grows on the surface of plants, obtaining nutrients from living epidermal cells from specialized structures known as haustoria that penetrate the cell walls and invaginate the cell membranes. PM fungi use the haustoria to obtain nutrients from living cells, but also to modulate the host plant’s defense responses. All plants have an immune system, and fungi that feed on living hosts use proteins known as effectors in order to inhibit host defense responses.

Control Strategies


As mentioned, it is important to control temperature and humidity. It is recommended to keep humidity low to control PM (20-40%RH). If PM is not such a big problem, keeping RH so low may not be recommended. I tend to try to keep RH in my grow tents around 40% RH. In addition to humidity in your grow area, it is important to have good airflow and ventilation. Every plant makes a microclimate around leaves [10]. The trichomes, hydrophobic leaf cuticle, and leaf transpiration create a small layer of air around leaves that is relatively still and higher humidity than surrounding air. Since this is the climate that PM spores and mycelium actually grows and reproduces in, it is important to disturb this microclimate with fans that gently disturb the leaves as well as to have high levels of air exchange in your grow area.

It is difficult to use temperature as a control method, as temperatures between 50 and 90 Farenheit (10-32 Celsius) can be conducive to PM growth and spread. Unfortunately, the high and low temperatures that may inhibit PM are also very stressful to Cannabis plants. I would recommend maintaining your normal temperatures (70-85 Farenheit or so), and focusing on humidity, circulation, and fresh air exchange in terms of climate control.

Genetic Resistance

One thing to consider is that the longer time a plant takes to achieve maturity, the more time PM has to develop and spread. Choosing plants with short flowering periods such as indica-heavy hybrids or short total growth periods such as autoflowering plants may be a good choice in reducing the risk of harvesting buds infected with PM.

PM disease resistance can indeed be bred for. Unless a major resistance gene is identified, it is likely that all resistance is multigene, quantitative resistance. Unfortunately there is not public research available as to which strains have high PM resistance. Research that has been done is likely by private companies and breeders screening commercial strains for PM resistance and keeping information in-house for a commercial advantage. Unfortunately, the strain selection here must be based on knowledge spread around the growing community on forums and growing websites such as this. It is important to note that these are anecdotes and have not been verified with any experiments.

Besides indica heavy strains being a better choice due to flowering time, it also appears that many strains with Afghani heritage are more resistant to PM than most strains. In general, landrace sativa strains from equitorial regions have higher mold (bud rot and fusarium) resistance than Afghanis. However, these strains also appear to be more susceptible to PM than many Afghani-dominant strains.

Here is a list of strains that I see popping up a lot when people discuss PM-resistant strains:

  1. Bubba Kush
  2. L.A. Confidential
  3. GDP
  4. Purple Punch
  5. Northern Lights
  6. White Widow
  7. Super Skunk
  8. White Russian
  9. Grape Ape
  10. Purple Kush

The one thing in common with all of these strains? Afghani Heritage. In fact, some of the most resistant strains also tend to have the most Afghani genetics. If you are selecting strains for PM resistance, a good rule of thumb is to maximize the Afghani landrance genetics by choose strains that are not just polyhybrids, but have had recent crosses with Afghani strains. Pairing proper selection of genetics with proper environmental controls will likely prevent you from having to deal with PM outbreaks. However, if you are still dealing with problems, you will have to move on to chemical control methods.


A few tips can help prevent a wide range of pest issues. If you are so able, isolate your grow area and use HEPA filters in your grow room, preferrably in your air intake. This will prevent spores from accessing your plants. UV lamps can also be installed in your ducting that are effective at killing airborne spores. All tools that you use for trimming, defoliating, or any plant manipulation should be soaked in a 70% alcohol solution before every use. After each cut, it should also be sprayed with the same solution and wiped dry. If possible, keep a box of nitrile or latex gloves close by and always wear them when entering the grow area. It would benefit you to not wear your outside clothes in your grow room. Have a pair of dedicated clothes for your grow area that you wash regularly.

Finally, sterilize your grow area after each harvest. Using 10% bleach can be one good way, but I would recommend cleaning your grow room once with a bleach solution, wipe it dry, and then do a second cleaning with a ‘Quat’ soap. If you follow the cultural, environmental, and strain selection guidelines I have put forth, you will likely not need any targeted fungicides (which are not approved for use in Cannabis at least at a commercial level, due to bureaucratic and legal reasons). However, I do recommend putting together a pest control spray program for your plants as well, for use in vegetative growth and even early flowering.


Unfortunately for commercial growers, there are very few registered fungicides that can be used on Cannabis. On the federal level, no pesticides have been approved for drug Cannabis. However, states have approved certain fungicides that the EPA has approved for hemp, which became federally legal in 2018.

If Cannabis is being sold on the legal markets and tests positive for an unapproved pesticide, it cannot be sold. Most of the fungicides on the market for Cannabis are not nearly as effective as fungicides used, for instance, in grape production for control of PM. The approved fungicides are generally untargeted, broad spectrum, and diversity of FRAC groups are not represented. Below is the list of approved fungicides in California:

• Bacillus amyloliquefaciens strain D747
• Cloves and clove oil
• Corn oil
• Cottonseed oil
Gliocladium virens
• Neem oil
• Peppermint and peppermint oil
• Potassium bicarbonate
• Potassium silicate
• Rosemary and rosemary oil
• Sodium bicarbonate
Reynoutria sachalinensis extract
Trichoderma harzianum

As you can tell, there are various fungi and bacteria that can be sprayed as biocontrol agents, plant extracts and oils, and some basic salts that can be sprayed. .

Compare what is available to be used on Cannabis with what is approved to be used for PM on another smokeable crop, tobacco, and you will see how handicapped the Cannabis industry is in terms of pest control options: Mancozeb, Terramaster, Azoxystrobin, Copper based fungicides, Actigard, Agri-Mycin, Manzate, Orondis, Aliette. It is likely that similar pesticides will eventually be approved for use in Cannabis on a federal level, though not until it is federally legal and goes through rigorous studies for pesticide safety. The EPA will not approve any pesticides for Cannabis if it remains a scheduled drug.

What do I use to address a PM outbreak and help prevent PM infection?

First, I want to address one common home remedy: milk. A lot of people swear by using diluted milk as a control method. In my experience, this is the least effective method out there. If you want to use something that basifies your leaf surface, I recommend using a baking soda (sodium bicarbonate) solution.


Many homegrowers swear by using baking soda or other bicarbonates (such as potassium bicarbonate which may be more effective than Sodium Bicarbonate). I believe that when used as a preventative, it is far more effective than to stop an outbreak. In my experience, once an outbreak starts, it may behoove you to go with more aggressive measures. Bicarbonate ions work by increasing the pH of the leaf surface which inhibits fungal growth/spore germination. It is best to include a spreader/sticker to your baking soda solution such as vegetable oil and dish soap without antibiotics.


  • 3 tbsp baking soda
  • 1 tbsp vegetable oil
  • a few drops of dish soap without antibiotics to emulsify the mixture.
  • *If you can get a nonionic surfactant such as Yucca extract or CocoWet, I would recommend that over dish soap which may have some amount of phytotoxicity. I would also recommend potassium bicarbonate over baking soda*

Spray liberally on your leaves, coating the tops and bottoms. This can be used on buds through harvest as well, though I would recommend rinsing your buds with water before harvesting.

Apply once per week as a preventative.

Neem Oil Products:

I would recommend to only use these during vegetative growth, pull back on use when buds begin to visibly form. Some have reported allergies to this product, and it may pose other health risks if ingested [11, 12].

  • During vegetative growth, neem oil should be sprayed as a preventative every 7-14 days depending on how aggressive you are trying to be in your disease control.
  • Generally it is recommended to use 2 tbsp of 70% neem oil concentrate for each gallon of water.
    • If you experience negative reactions in your plants, try diluting it further to about 1 tbsp/gal.
    • I like to add just a couple of drops of dishwashing soap to help emulsify the oil.
  • Use a one-hand pressure sprayer to fully coat the tops and bottoms of all of the leaves of your plant.
  • Spray your plants at night, just after the sun sets so that there is plenty of time for the leaves to dry
    • If it is not dry by the time the sum comes out, your leaves can get sunburned quite easily, make sure you have plenty of fans moving and drying your leaves
  • About 3 days after your neem oil application, rinse your leaves with water or a solution of citric acid pesticide such as Nuke Em by Flying Skull or other comparable products.
    • I like to rinse just to prevent buildup of oils, but this is not necessarily required, in fact having the oil on the leaves can help deter insects. You could also just do a rinse right before your next application.
  • If you are experiencing an outbreak, begin using it more frequently, up to once every 5 days.
  • Purified azadirachtin products, while useful for insects, are not as useful for PM. The main ingredients in neem oil that are effective against PM are the triglycerides and terpenes that are not present in products like Azamax.
  • Stop using it when you see buds beginning to form (not right when flowering starts, but you don’t want neem residue on your buds)

Citric Acid

Some have reported that citric acid sprays are not as effective at controlling powdery mildew outbreaks as compared to other fungicides, but I believe that they can be effective when used in an IPM program with other fungicides. It is important to use what we have available since there are few targeted pesticides available for use in Cannabis.

  • Some studies have shown that citric acid can significantly reduce the incidence of PM [13] (though there are no studies on Cannabis specifically)
  • Citric acid sprays (especially solutions such as Nuke Em that also have insecticidal soaps and yeast) have the added bonus of helping to control insects including aphids, whiteflies, and arthropods such as mites.
  • Finally, citric acid may be able to increase yield of your plants, including dry flower weight [14, 15].
  • You can continue to use citric acid all through flower, and some people even spray it on their buds at harvest to help prevent postharvest bud rot without any noticeable change in flavor or bud quality.
  • I would not use this in an IPM program along with baking soda solutions, because both affect the pH of your leaf surface in different directions.

Plant Extract Oils

There are some approved plant extracts described in my list of approved pesticides. I have never tried these for powdery mildew, but it may be worth trying. There are some products that have premixed a variety of different oils.

For instance, Trifecta crop control has the following ingredients:

14.0%……….Thyme Oil
10.0%……….Clove Oil
9.0%…………Garlic Oil
4.0%…………Peppermint Oil
3.0%…………Corn Oil
2.0%…………Citric Acid
2.0%…………Rosemary Oil

However, this product, as well as neem oil, has the potential for causing some foliar stress symptoms until the plant becomes acclimated. It would be interesting to make a mix of Trifecta as well as Neem oil and replacing the pure neem spray with this mixture.

Again, I am not sure as to the efficacy of mixing this with neem. I have seen many forums of people claiming that this is a helpful product for controlling insects, though I have not seen much information for how it works on PM.

Reynoutria sachalinensis Extract

Reynoutria sachalinensis is a plant from which extracts are made. Extracts are classified as ‘plant activators’, meaning that the compounds stimulate the SAR (systemic acquired resistance) and ISR (induced systemic resistance) responses of plants. In short, this means that resistance genes in the plant are induced prior to any pathogen recognition, essentially making the plant more resistant to attack. I definitely recommend using this, and I believe it can be worked into a good IPM program. This, much like citric acid sprays, can be used up to the day of harvest.

B. subtilis Spray

Finally, I recommend adding a biofungicide (applying a spray with living microorganisms). The most common biofungicides utlize Bacillus subtilis bacteria or Trichoderma harzianum fungi. In general, B. subtilis is used as a foliar spray, and T. harzianum is used as a soil soak, mainly to control soil pathogens. However, there is evidence that using T. harzianum to the soil can actually increase the efficacy of B. subtilis foliar sprays [16,17], though I recommend sticking to B. subtilis sprays unless you are growing outdoors and concerned about soil pathogens. Such products include Serenade and Cease.

Keep in mind that B. subtilis in not labeled for Cannabis use in CA, if you want to use a Bacillus spray that is on-label, use B. amyloliquefaciens such as Revitalize or Triathlon.

Hydrogen Peroxide

Hydrogen Peroxide can be good for when an outbreak is actively occurring. If I could recommend one product for sanitation purposes, it would be Zerotol. Not only does it have hydrogen peroxide, but it also has peroxyacetic acid. Peroxyacetic acid forms when acetic acid (vinegar) reacts with hydrogen peroxide. Both of these are strong oxidizing agents that will kill the fungus on contact without harming your plants. As these products degrade, they will form water, carbon dioxide, and water. Peroxyacetic acid can be corrosive and dangerous in high concentrations, so be sure to dilute it according to producer recommendations. In the midst of an outbreak, this can be used every 3-5 days to help control the pathogen outbreak. This is a particularly effective tool for when an outbreak occurs in flower.

One preventative IPM program centered around PM might look like this:

Day 1: Neem Oil or Azadirachtin Spray/Plant Oil Extract Spray (or mixture)

Day 4: Citric Acid/Insecticidal Soap spray such as Nuke Em (to rinse neem oil) or sodium bicarbonate mixture outlined previously.

Day 7: Regalia Spray

Day 10: Restart Cycle.

Another rotation might look like:

Day 1: Neem Oil or Azadirachtin Spray/Plant Oil Extract Spray (or mixture)

Day 4: Citric Acid/Insecticidal Soap spray such as Nuke Em (to rinse neem oil) or sodium bicarbonate mixture outlined previously.

Day 7: Serenade Spray

Day 10: Restart Cycle.

You can also make tank mixes of Serenade and Regalia, or replace the neem oil with one or the other, especially after stopping using oil sprays in flower.

  1. Punja, Z. K. (2018). Flower and foliage-infecting pathogens of marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology, 40(4), 514–527. https://doi.org/10.1080/07060661.2018.1535467
  2. Weldon, W. A., Ullrich, M. R., Smart, L. B., Smart, C. D., & Gadoury, D. M. (2020). Cross-Infectivity of Powdery Mildew Isolates Originating from Hemp (Cannabis sativa) and Japanese Hop (Humulus japonicus) in New York. Plant Health Progress, 47–53. https://doi.org/10.1094/PHP-09-19-0067-RS
  3. Szarka, D., Tymon, L., Amsden, B., Dixon, E., Judy, J., & Gauthier, N. (2019). First Report of Powdery Mildew Caused by Golovinomyces spadiceus on Industrial Hemp (Cannabis sativa) in Kentucky. Plant Disease, 103(7), 1773. https://doi.org/10.1094/PDIS-01-19-0049-PDN
  4. Félix-Gastélum, R., Olivas-Peraza, D. D., Quiroz-Figueroa, F. R., Leyva-Madrigal, K. Y., Peñuelas-Rubio, O., Espinosa-Matías, S., & Maldonado-Mendoza, I. E. (2019). Powdery mildew caused by Golovinomyces spadiceus on wild sunflower in Sinaloa, Mexico. Canadian Journal of Plant Pathology, 41(2), 301–309. https://doi.org/10.1080/07060661.2019.1577916
  5. Félix-Gastélum, R., Olivas-Peraza, D. D., Quiroz-Figueroa, F. R., Leyva-Madrigal, K. Y., Peñuelas-Rubio, O., Espinosa-Matías, S., & Maldonado-Mendoza, I. E. (2019). Powdery mildew caused by Golovinomyces spadiceus on wild sunflower in Sinaloa, Mexico. Canadian Journal of Plant Pathology, 41(2), 301–309. https://doi.org/10.1080/07060661.2019.1577916
  6. Dahlia – Plant Parasites of Europe. (n.d.). Retrieved February 13, 2020, from https://bladmineerders.nl/host-plants/plantae/spermatopsida/angiosperma/eudicots/superasterids/asterids/campanulids/asterales/asteraceae/asteroideae/coreopsineae/dahlia/
  7. Humidity | North Carolina Climate Office. (n.d.). Retrieved February 13, 2020, from https://climate.ncsu.edu/edu/Humidity
  8. Guzman-Plazola, R. A., Davis, R. M., & Marois, J. J. (2003). Effects of relative humidity and high temperature on spore germination and development of tomato powdery mildew (Leveillula taurica). Crop Protection, 22(10), 1157–1168. https://doi.org/https://doi.org/10.1016/S0261-2194(03)00157-1
  9. Sunflower (Helianthus spp.)-Powdery Mildew | Pacific Northwest Pest Management Handbooks. (n.d.). Retrieved February 14, 2020, from https://pnwhandbooks.org/node/3589/print
  10. Aust, H., & Hoyningen-Huene, J. V. (1986). Microclimate in Relation to Epidemics of Powdery Mildew. Annual Review of Phytopathology, 24(1), 491–510. https://doi.org/10.1146/annurev.py.24.090186.002423
  11. Bhaskar, M. V, Pramod, S. J., Jeevika, M. U., Chandan, P. K., & Shetteppa, G. (2010). MR imaging findings of neem oil poisoning. American Journal of Neuroradiology, 31(7), E60–E61.
  12. Neem Oil General Fact Sheet. (n.d.). Retrieved February 7, 2020, from http://npic.orst.edu/factsheets/neemgen.html
  13. Jafari, N., & Hadavi, E. (2011). Growth and essential oil yield of dill (Anethum graveolens) as affected by foliar sprays of citric acid and malic acid. I International Symposium on Medicinal, Aromatic and Nutraceutical Plants from Mountainous Areas (MAP-Mountain 2011) 955, 287–290.
  14. Talebi, M., Hadavi, E., & Jaafari, N. (2014). Foliar Sprays of Citric Acid and Malic Acid Modify Growth, Flowering, and Root to Shoot Ratio of Gazania (Gazania rigens L.): A Comparative Analysis by ANOVA and Structural Equations Modeling. Advances in Agriculture, 2014, 147278. https://doi.org/10.1155/2014/147278
  15. Ghazijahani, N., Hadavi, E., & Jeong, B. R. (2014). Foliar sprays of citric acid and salicylic acid alter the pattern of root acquisition of some minerals in sweet basil (Ocimum basilicum L.)  . In Frontiers in Plant Science  (Vol. 5, p. 573). https://www.frontiersin.org/article/10.3389/fpls.2014.00573
  16. Zaim, S., Bekkar, A. A., & Belabid, L. (2018). Efficacy of Bacillus subtilis and Trichoderma harzianum combination on chickpea Fusarium wilt caused by F. oxysporum f. sp. ciceris. Archives of Phytopathology and Plant Protection, 51(3–4), 217–226. https://doi.org/10.1080/03235408.2018.1447896
  17. Maketon, M., Apisitsantikul, J., & Siriraweekul, C. (2008). Greenhouse evaluation of Bacillus subtilis AP-01 and Trichoderma harzianum AP-001 in controlling tobacco diseases. Brazilian Journal of Microbiology : [Publication of the Brazilian Society for Microbiology], 39(2), 296–300. https://doi.org/10.1590/S1517-838220080002000018

1i. McPartland, J. M. (1991). Common names for diseases of Cannabis sativa L. Plant Disease, 75, 226–227.
2i. McPartland, J. M. (n.d.). A review of Cannabis diseases. Retrieved February 5, 2020, from http://druglibrary.org/olsen/hemp/iha/iha03111.html

How Do I Germinate Cannabis Seeds and Transplant Clones?

Clones vs Seedlings

Clones and seedlings may seem very similar, but there are some differences between the two starting points. First of all, seedlings (small plants sprouted from seed) have a taproot. This is a central dominant root that tends to grow straight down and proliferate the branching root structures that explore the growing medium. Clones do not have a taproot; instead, they immediately begin producing a fibrous branching root structure. I would argue that the taproot is most important in outdoor grows due to the higher degree of anchoring and stem support that it can provide in windy weather.

Secondly, seeds all have unique genotypes while clones have the same genotype as the mother plant they were cut from. Truly stable seed lines produce plants with phenotypes so similar that they could be mistaken for clones, but usually in the Cannabis industry, a given seed pack for a strain may produce multiple different phenotypes. Sometimes this can be desirable if you are phenotype hunting for a unique plant to grow or breed with, but at least in large scale production, uniformity is usually preferred because it simplifies the growing, harvesting, and processing techniques

How Do I Germinate Seeds?

There are many ways to skin this particular cat. First of all, it is important to consider the environmental conditions required for germination.


While some small seeds without much of a starch reserve require light to germinate, it appears that light actually inhibits the germination of Cannabis seeds. This is likely due to the red light sensing system by light-sensing proteins called phytochromes. In general, far-red light can penetrate further into soil than red light due to the longer wavelength. Plants often utilize the ratio of far red light to red light as a way to sense depth in soil. For Cannabis, it appears that it requires a low far red/red ratio (no to minimal light) in order to germinate. However, pure darkness is unnecessary in my experience. In fact, it is a bit of a balancing act because after germination, your seedlings require light or they will not begin to produce chlorophyll and will continue to etiolate (grow and stretch in search of light to begin photosynthesis). Therefore, you will need to check your seedlings frequently so if you germinate in complete darkness, you can quickly introduce your newly sprouted seedlings to light.

Moisture and Humidity

Seedlings require water uptake in order to trigger germination. The media they are in contact with should be moist, and the humidity should be kept high but ventilated to help prevent microbial growth. In general, this translates to around 70-90% humidity. However, I don’t generally keep track of the humidity of the air in my germination area. Humidity is ensured to be high by enclosing the germination medium with a ziploc bag with holes cut in it.


I like to follow the rule of thumb: keep the temp in the 70s throughout the day and night. Don’t let temperatures dip below 70F and don’t let temperatures rise above 80F. In Celsius, this translates to approximately 21-27C. In practice, it is okay if it gets warmer, though I certainly would avoid letting temperatures get above 30C (86F). However, high heat can inhibit germination and encourage microbial growth. Also, dipping below 70F does not ensure failure, but may not be as efficient at germinating seeds.

I will only cover 2 germination methods. This is because in my opinion, they are simple, effective, and I have experience in both.

Method 1: Wet Paper Towel.

Get a paper towel and soak it in water (it is probably ideal if you get sterile, deionized water, though I generally use tap water and it works just fine). Squeeze out the paper towel so that it is damp but not wet. Place your seeds on the damp paper towel, and fold the paper towel one time over the seed. Place the folded paper towel in a gallon size plastic bag.

Option 1: Poke a few holes in the plastic bag (I like to use sharpened pencils, it has a good size for holes), blow into the bag to ensure it’s not collapsed on the paper towel, seal the bag, and place it in a dark, warm place. Check daily for germination and make sure to keep the paper towel moist. If it gets too dry, just use a spray bottle to spritz the inside of the bag and paper towel.

Option 2: Don’t poke any holes, exchange the air inside by sucking the air out the bag and blowing back into it to inflate it. Seal the bag, place it in a cool, dark place, and exchange the air in the bag once to twice/day and check frequently for germination.

Transplanting Germinated Seeds

After germination, I like to wait until the taproot is about an inch long. After this, pick it up by the seed coat with tweezers or a very gentle touch. Don’t touch the taproot. take your soil or growing medium, moisten it using appropriately pH’d water (around 6.5 for soil) and prepare a a hole deep enough to place the germinated seed in with the taproot facing down and the seed coat barely below the soil line. Place the seed in so that the taproot is straight down and so that the tip of the taproot is not bent or hooked when you plant it.

Method 2:

Plant your seed directly in a seed starter (I like to use coco coir with a bit of mycorrhizal fungi sprinkled in).

Option 1 is to buy seed starter coco coir pellets. All that is required is to wet the pellets with properly pH’d sterile water. They will expand and will have a small hole in the center for you to place your seed. After planting your seed, gently cover it up. This will provide both light and local humidity around your seed. Cover the pellet loosely with an open plastic bag to help retain moisture and leave it on a windowsill or under artificial light. This will ensure that once the seed germinates under the soil which is dark and humid, it will sprout above the ‘soil’ line, remain in a humid environment in the plastic bag , and will also be exposed to light so that the seedling can begin photosynthesis. I do not like to use peat moss or peat-based pellets such as Jiffy pellets. First of all, coco coir is far more environmentally friendly because peat is a nonrenewable resource, unlike coco coir. I stay away from rock wool for the same reason, coco coir is just a more responsible consumer choice for the environment. Secondly, peat is extremely acidic and may affect nutrient uptake early in a plant’s life as compared to coco coir. For all seed starting mixes, I like to make about a quarter of the volume perlite. Seedlings do not uptake water well and you want good soil aeration to avoid damping off and root rot diseases. If you use premade pellets, you will not have this option.

Option 2 is to fill a small, 2-3 oz plastic cup with coco coir, moisten it and make a hole for the seed yourself, and sow your seed. Follow the same directions as outlined for the pellets.

What do I do now that my seedling has germinated?

Now that you have a germinated seedling, you will notice two small ‘leaves’ that are kind of oval-shaped. These are known as cotyledons, and can actually help provide your plant with nutrients that were stored in the seed until the plant can feed on fertilizer or nutrients in soil depending on your growing style.


You will want to provide your plant with enough light to not stretch out. You can get away with using even a 60W single CFL ‘grow’ bulb for a seedling, but I tent to keep my seedlings under a 300W LED panel. I like to keep the light source about a foot from the top of my seedling.


Go ahead and keep the temperatures in the 70s (Farenheit). This is a great range for Cannabis growth and isn’t as conducive to disease development as warmer temperatures.


You will want to slowly lower the relative humidity. Keeping the same level of humidity as for germination will prove to be too conducive to disease development especially seedling damping off and root rots. Go ahead and keep the plastic bag over the seedling at first, and slowly increase the amount of time each day that it is not under the plastic bag. In general, I like to leave the bag off the seedling at night after it sprouts and during the day, reduce the time it is under the bag by an hour each day until the second set of true leaves are visible, then remove it altogether.

Moisture and Feeding

Seedlings require more moisture that mature plants but you also want to avoid root rots. Therefore, I like to use a spray bottle to mist the soil every day without soaking it. This should be done until the second set of true leaves are visible, then begin your normal watering schedule. Your seed starter mix should not have fertilizer in it. Your plant should have all the nutrients it needs from the cotyledons and all the energy it needs from photosynthesis. However, after the first true leaves are fairly large and the second set of true leaves are barely visible, I will sometimes include a Nitrogen dominant fertilizer at 1/4 strength in the spray bottle and lightly mist until slightly damp (I only ever do this once before transplanting, and only if the leaves are looking light). I tend to use liquid fertilizers (you can find conventional or organic fertilizers depending on your fancy).

Transplanting Your Seedling

By the time the second set of true leaves have grown in, your seed starter plug should be colonized by roots. Or, if you purchased a clone, it is likely already rooted in a rock wool cube. Take a pot approximately 10x the volume of your rooting medium, fill it with the planting medium of your choice (soil or soilless medium[if soilless, it is a good idea to do a light feeding (1/4 strength) as well at this point]). Water the medium in your new pot before transplanting and allow it to drain to field capacity. Make a crater in the center of your moistened medium deep enough to completely cover the seedling medium. I like the lowest nodes on the plant to be about 1-2″ above the soil line after planting. Place in your rooting plant, fill in the crater, smooth it out, and lightly pack in the planting medium around the stem of your plant. Water the pot once more to ensure the soil settles in, allow it to drain capacity.

Congratulations, you have germinated your seed and/or transplanted your clone/seedling. That was pretty easy, right?

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