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broad mite damage on cannabis

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.
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

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.

Symptoms

  • *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).
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.
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)

Identification

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].

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].

Symptoms

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].

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.

Mites on carrier for sprinkling on plants:

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:

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.

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

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.

Fungi

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

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.

Bacteria

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.

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.

Chemical Control

Sulfur

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.)

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.

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):

Pyrethrins

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 BrandPyrethrin & 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.

Mighty is not found on Amazon. Purchase from NPK Industries

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.

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].

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.

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.

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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.

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 BrandPyrethrin & Insecticidal Soap concentrate.

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 ( 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

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… ]]>