Pests & Disease

If you see bugs on your plants, don’t start thinking they are good bugs helping to grow your crop grow big fat nugs.  They are there to suck the life out of them, either from the roots, stems, or leaves.  Before we start talking about chemicals and other means of pest management, there are ways to stop the bugs from ever getting up in your grow in the first place

Companion plating is a method of planting two or more plants in close proximity to encourage beneficial relationship. There are different types of companion planting that have different goals.

Trap Cropping

            Trap cropping is planting a sacrificial crop called “trap-crop.”  The trap crop becomes a lure for pest to save the more valuable crop.  The most important factor to consider when trap cropping is the pest you are trying to lure. Different crops attract different pests, so it is important to research this and choose the appropriate crop. Here are some possible plants you can use.

Pest Trap Crop
Aphids Nettles (early season)/ Nasturtium
Blackfly Nasturtium
Greenfly Nasturtium
Whitefly Nasturtium
Slugs Chervil/ French Marigold
Thrips French Marigold/ Basil
Flea Beetle Radish
Root Maggot/Fly Radish
Leafhopper Beans/Legumes
Tomato Hornworm Dill/ Lovage/ Beans
Nematodes African Marigolds Tagetes erecta
Cucumber beetle Nasturtium/ Blue Hubbard Squash
Squash vine borer Nasturtium/ Blue Hubbard Squash

The trap crop should be about 15%-20% of the main crop. If your trap crop becomes overrun with pests, sometimes it is best that you remove it before the bugs spread to your buds.

Nurse Cropping

Nurse cropping is planting multiple crops close together to gain mutual benefits as they grow together. One example is planting pole beans, corn, and squash together. The pole beans can climb the young corn stalks, allowing them to have better access to the sun and mature early. The beans will then die off and promote nitrogen uptake from the soil which is demanded by corn. At the same time, the squash will prevent weed overgrowth and protect the corn from pest such as raccoons.  Don’t try this with cannabis, it won’t work.

Intercropping

            Intercropping is a type of companion planting that helps increase crop yield and promote biodiversity. This is done by planting crops in close proximity where they can benefit from each other. Different crops have different roles and different nutrient needs. A healthy biodiversity will attract pollinators and pest predators. It is important that you study each plant and make sure that they will not compete each other’s needs. You can also plant short season crops and long season crops together. This will allow to have a continuous harvesting seasons maximizing your time.   This is also useless for cannabis cultivation, but I thought you should know just the same lol.

Integrated Pest Management

Integrated Pest Management (IPM) is using knowledge and resources to create steps in reducing the risk of plant pests and crop damage.

Prevention

Everything starts at prevention.  Preventing a disease is easier than trying to cure it.  Here are some steps you can take to prevent pest infestation.

  • Cleanliness – Keep your garden space free from debris, weeds, water, and other equipment.   That means you need to clean it, jackass.  Also make sure that there is free space between crops to allow airflow and stop the spread of insects from one plant to another.
  • Preventive plant treatment – when you get new plants from other sources. It is important to quarantine and treat them before introduction into your garden.
  • Preventive room treatment – it best to use a can of fogger like Dr. Doom or spray Physan 20 around thoroughly in empty grow areas to get better results. Use foggers before you use an empty grow area.

Scouting and Monitoring

It is best to know the common insects in your environment. Identify the helpful and harmful insects. Knowing the pests that are commonly present in your area can help prepare in fighting them.

The most common pest are spider mites, thrips, root aphids, fungus gnats, whiteflies, russet mites, and foliar aphids.

Regular inspection can help prevent damage or possible death to your crops.

Treatment of an Infestation

There will always be time when an infestation gets through all your preventive measures. It is also best to be prepared when this happens to prevent further damage. Knowing the right products for the right pest is important.

Remove Affected Parts From The Plant

If part of your plant or plants are showing signs of mites or other parasitic insects on only parts of the plant, it is a good first step to remove any affected areas of the plant by defoliating(removing leaves) that are visibly being attacked.  If the whole plant is affected, don’t rip everything off to the stems, the plant will die, but you might want to at least remove the worst areas to get a head start before treating with sprays of any kind.

Biological Treatment

Pest also have natural enemies. Beneficial Insects, fungi, and bacteria are sometimes effective in both preventing and treating various pests.  Here are some of the common biological treatments:

  • Phytoseiulus persimilis(predatory mite) for controlling spider mites
  • Botanigard ES and Met-52 for controlling root aphids
  • Gnatrol WDG,Nematodes, and Bacillus Thurenginnis for controlling fungus gnats
  • Encarsia formosa for controlling whiteflies
  • Ladybugs for controlling aphids primarily and mites secondarily
  • Amblyseius cucumeris for controlling thrips.

Organic Pesticides

For a pesticide to be organic, it doesn’t need to have an OMRI certificate or other qualified organization’s certification, but you can trust these products have been tested to be sure they contain only organic ingredients.  Organic pesticides are the safest to use since they don’t have high risk to humans from either direct contact, or any risk from consumption of plants exposed to the organic pesticide.  Personal protective equipment is still needed, so please refer to the instructions on the organic pesticide being used.

Synthetic Pesticides

There are also artificial pesticides that can be used, but it is best to know the  effects of the product you are using, as some can be harmful to humans, pets, and aquatic wildlife.

Spider Mite Treatment

Spider mites are by far the most common annoyance for marijuana growers.

Quick Facts…

  • Spider mites are common plant pests. Symptoms of injury include flecking, discoloration (bronzing) and scorching of leaves. Injury can lead to leaf loss and even plant death.
  • Natural enemies include small lady beetles, predatory mites, minute pirate bugs, big-eyed bugs and predatory thrips.
  • One reason that spider mites become a problem is insecticides that kill their natural predators.
  • Irrigation and moisture management can be important cultural controls for spider mites.
Honeylocust spider mites

Figure 1: Honeylocust spider mites, with eggs.

Spider mites are common pest problems on many plants around yards and gardens in North America. Injury is caused as they feed, bruising the cells with their small, whiplike mouthparts and ingesting the sap. Damaged areas typically appear marked with many small, light flecks, giving the plant a somewhat speckled appearance.

Following severe infestations, leaves become discolored, producing an unthrifty gray or bronze look to the plant. Leaves and needles may ultimately become scorched and drop prematurely. Spider mites frequently kill plants or cause serious stress to them.

Spider mites (Family: Tetranychidae) are classed as a type of arachnid, relatives of insects that also includes spiders, ticks, daddy-longlegs and scorpions. Spider mites are small and often difficult to see with the unaided eye. Their colors range from red and brown to yellow and green, depending on the species of spider mite and seasonal changes in their appearance.

Many spider mites produce webbing, particularly when they occur in high populations. This webbing gives the mites and their eggs some protection from natural enemies and environmental fluctuations. Webbing produced by spiders, as well as fluff produced by cottonwoods, often is confused with the webbing of spider mites.

The most common spider mite found on cannabis is the twospotted spider mite (Tetranychus urticae). This mite attacks a wide range of garden plants, including many vegetables (e.g., beans, eggplant), fruits (e.g., raspberries, currants, pear) and flowers. The twospotted spider mite is also the most important species on house plants. It is a prolific producer of webbing.

 

Spider Mites with eggs

Figure 2: Twospotted spider mites, with eggs.

Life History and Habits

Spider mites develop from eggs, which usually are laid near the veins of leaves during the growing season. Most spider mite eggs are round and extremely large in proportion to the size of the mother. After eggs hatch, the old egg shells remain and can be useful in diagnosing spider mite problems.

There is some variation in the habits of the different mites that attack garden plants, trees and shrubs. Outdoors, the twospotted spider mite and honeylocust spider mite survive winter as adults hidden in protected areas such as bark cracks, bud scales or under debris around the garden. Other mites survive the cool season in the egg stage. As winter approaches, most mites change color, often turning more red or orange. This habit may be why they are sometimes called “red spiders.”

Most spider mite activity peaks during the warmer months. They can develop rapidly during this time, becoming full-grown in as little as a week after eggs hatch. After mating, mature females may produce a dozen eggs daily for a couple of weeks. The fast development rate and high egg production can lead to extremely rapid increases in mite populations.

Other species of spider mites are most active during the cooler periods of the growing season, in spring and fall. This includes the spruce spider mite and most of the mites that can damage turfgrass. These cool-season spider mites may cease development and produce dormant eggs to survive hot summer weather.

Dry conditions greatly favor all spider mites, an important reason why they are so common in the more arid areas of the country. They feed more under dry conditions, as the lower humidity allows them to evaporate excess water they excrete. At the same time, most of their natural enemies require more humid conditions and are stressed by arid conditions. Furthermore, plants stressed by drought can produce changes in their chemistry that make them more nutritious to spider mites.

Control

Biological Controls

Various insects and predatory mites feed on spider mites and provide a high level of natural control. One group of small, dark-colored lady beetles known as the “spider mite destroyers” (Stethorus species) are specialized predators of spider mites. Minute pirate bugs, big-eyed bugs (Geocoris species) and predatory thrips can be important natural enemies.

Spider Mite

Figure 3: Twospotted spider mite injury to eggplant.
Lady Beetle

Figure 4: “Spider mite destroyer” lady beetle.
Minute pirate bug

Figure 5: Minute pirate bug.

A great many mites in the family Phytoseiidae are predators of spider mites. In addition to those that occur naturally, some of these are produced in commercial insectaries for release as biological controls. Among those most commonly sold via mail order are Galendromus occidentalisPhytoseiulus persimilisMesoseiulus longipes and Neoseiulus californicus. Although these have been successful in control of spider mites on interior plants, effective use outdoors has not been demonstrated in Colorado. Predatory mites often have fairly high requirements for humidity, which can be limiting. Most suppliers provide information regarding use of the predator mites that they carry.

One reason that spider mites become problems in yards and gardens is the use of insecticides that destroy their natural enemies. For example, carbaryl (Sevin) devastates most spider mite natural enemies and can greatly contribute to spider mite outbreaks. Malathion can aggravate some spider mite problems, despite being advertised frequently as effective for mite control. Soil applications of the systemic insecticide imidacloprid (Merit, Marathon) have also contributed to some spider mite outbreaks.

Water Management

Adequate watering of plants during dry conditions can limit the importance of drought stress on spider mite outbreaks. Periodic hosing of plants with a forceful jet of water can physically remove and kill many mites, as well as remove the dust that collects on foliage and interferes with mite predators. Disruption of the webbing also may delay egg laying until new webbing is produced. Sometimes, small changes where mite-susceptible plants are located or how they are watered can greatly influence their susceptibility to spider mite damage.

Chemical Controls

Chemical control of spider mites generally involves pesticides that are specifically developed for spider mite control (miticides or acaricides). Few insecticides are effective for spider mites and many even aggravate problems. Furthermore, strains of spider mites resistant to pesticides frequently develop, making control difficult. Because most miticides do not affect eggs, a repeat application at an approximately 10- to 14-day interval is usually needed for control. Table 1 includes a summary of pesticides that may be useful for managing spider mites.

Control of Spider Mites on Cannabis Plants

Control on cannabis plants can be particularly frustrating. There generally are no biological controls and few effective chemical controls (primarily soaps and horticultural oils). When attempting control, treat all susceptible plants at the same time. Trim, bag and remove heavily infested leaves and discard severely infested plants. Periodically hose small plants in the sink or shower. Wipe leaves of larger plants with a soft, damp cloth. Reapply these treatments at one- to two-week intervals as long as populations persist.

Table 1: Pesticides useful to control spider mites in yards and gardens.
Active Ingredient Trade Name(s) Comments
acephate Orthene, certain Isotox formulations Insecticide with some effectiveness against spider mites. Systemic.
abamectin Avid For commercial use only on ornamental plants. Primarily effective against twospotted spider mite; less effective against mites on conifers. Limited systemic movement.
bifenthrin Talstar, others Insecticide with good miticide activity.
hexythiazox Hexygon For commercial use only on ornamental plants. Selective miticide that affects developing stages and eggs only. One application per season label restriction.
horticultural oils Sunspray, others Used at the “summer oil” rate (2 percent), oils are perhaps the most effective miticide available for home use.
insecticidal soap several Marginally effective against twospotted spider mite and where webbing prevents penetration. Broadly labeled.
spiromesifan Forbid For commercial use only on ornamental plants. Selective against mites and conserves natural enemies.
sulfur various Generally sold in dust formulation for control of various fungal diseases and some mites on some ornamental and vegetable crops.

Helpful Hints:

  • Water all plants thoroughly before applying any foliar spray.
  • Cover sensitive surfaces, such as food preparation areas.
  • Close and shut off air conditioning or ventilating equipment if indoors.
  • Shake or stir mixture fully before using, and shake every few minutes during spraying.
  • Completely drench tops and undersides of all leaves and stems of every plant in the room with spray mixture, to the point of dripping.
  • Smaller plants can be fully submerged in the mixture to ensure total coverage.
  • Turn lights off, or spray at night for outdoor applications.  It is highly recommended to spray during darkness with a green light, or under dim light to reduce plant phytotoxicity.
  • Spray walls, ceiling and floors for added protection.
  • If there are plants in other rooms that don’t appear to be affected by mites, it is still recommended that they be sprayed as a precaution so they don’t become a new target host.
  • Cooler temperatures & low humidity will slow mite activity & reproduction.
  • Removing any damaged, dead, or dying leaves will increase your plants natural resistance to mites.  Remove & discard as many mite infested leaves as possible before spraying.  A vacuum can be used to remove mite webbing from tops of plants.
  • If using beneficial insects, apply them after spraying any miticide/insecticide.
  • Never spray wilting, wilted, or dry plants.  Water first and wait for turgidity to be restored in stems and leaves.
  • Fogging may create a slippery layer on surfaces, and full ventilation before reoccupying is recommended.

Managing Key Pests of the Crop

Azadirachtin

This is the primary insecticidally active ingredient extracted from the seeds of the neem tree (Azadirachta indica). The primary effect on susceptible insects is to disrupt growth by interfering with molting. Insect groups against which it has been shown to have some effectiveness for control include certain Lepidoptera, Diptera, Hemiptera, Coleoptera, and Thysanoptera.

Potential Use in Colorado Cannabis Pest Management. Soil drenches of azadirachtin have some proven value in control of fungus gnat larvae. It is possible that azadirachtin could be useful in suppressing rice root aphid, but this is untested. It is also used for control of cannabis aphid and whiteflies. It has shown some modest effect on some grasshoppers and flea beetles and may be useful for controlling some caterpillar pests of the crop, such as corn earworm. Azadirachtin has not been found effective for control of spider mites in research trials.

Azadirachtin-containing insecticides include: Aza-Direct Biological Insecticide, AzaGuard, AzaMax, AzaSol, Azatrol EC, Azatrol Hydro Botanical Insecticide, Azatin O Biological Insecticide, Azera Insecticide, Azera Gardening, BioSafe Insect Control, Debug Turbo, Ecozin Plus 1.2% ME, Ornazin 3% EC Botanical Insecticide, Safer Brand BioNeem, Molt-X, Neemix 4,5 Insect Growth Regulator, The Ecology Works SoluNeem.

Potassium Salts of Fatty Acids (Insecticidal Soaps, Potassium Laurate)

Liquid soaps derived from certain fatty acids produce soaps that are insecticidally active. Diluted with water, typically to a 1-3% solution, they are contact insecticides that can kill certain insects and mites if sprays contact the insect at application. There is no residual activity. Insecticidal soaps have primarily been used to control certain small, soft-bodied insects and mites that are exposed on plants.

Potential Use in Colorado Cannabis Pest Management. Label uses include aphids, whiteflies and some species of spider mites and rust mites. Sprays of soaps may have some suppressing effect on twospotted spider mite and hemp russet mite; label uses include some species of spider mites and rust mites. However, in other crops insecticidal soaps are generally considered only marginally effective for mite control.

Potassium salts of fatty acid pesticides (insecticidal soaps) include: Bayer Advanced NATRIA Insecticidal Soap, Bonide Insecticidal Soap, Des-X Insecticidal Soap, Earth-tone Insecticidal Soap, General Hydroponics Exile Insecticide/Fungicide/Miticide, Hydro Worxx Insecticidal Soap, Kopa Insecticidal Soap, Miracle-Gro Nature’s Care Insecticidal Soap, M-Pede Insecticidal Soap, Natural Guard Insecticidal Soap, Nuke Em, Ortho Elementals Insecticidal Soap, Safer Brand insecticidal Soap, Sil-Matrix, Schultz Garden Safe insecticidal Multi-Purpose, Whitney Farms Insecticidal Soap, Worry Free Brand Insecticidal Soap.

Bacillus thuringiensis var. kurstaki

This is a strain of the soil bacterium Bacillus thuringiensis that produces proteins that, when ingested, are capable of killing susceptible insects by destroying cells of the midgut. The kurstaki strain is specific in its effects with certain insects in the order Lepidoptera (caterpillars).

Potential Use in Colorado Cannabis Pest Management. Caterpillars are normally not important in indoor production of Cannabis. However, some caterpillar pests are a potential pests in outdoor production, particularly corn earworm which can tunnel into developing buds. Other caterpillars that are pests of the crop that may be managed with appropriately timed applications include beet armyworm, beet webworm, woollybears, and Eurasian hemp borer.

Bacillus thuringiensis var. kurstaki pesticides include: Biobit HP Biological Insecticide, Crymax, Deliver Biological Insecticide, Dipel DF Biological Insecticide, Foray XG Insecticide Flowable Concentrate, Javelin WG Biological Insecticide, Valent Professional Products DiPel Pro DF Biological Insecticide

Beauveria bassiana

Beauveria bassiana is a fungus that is capable of producing disease in a great many kind of insects. Commercial formulations are applied as sprays that contain spores of the fungus. If environmental conditions are favorable, with high humidity being particularly important, the spores will germinate on the surface of the insect then may successfully invade and infect the insect. Infected insects usually will die within a week of application. Both presently allowed Beauveria bassiana insecticides also contain pyrethrins (see below) which has a very different mode of action.
Potential Use in Colorado Cannabis Pest Management: Due to the humidity requirement for spore germination, Beauveria bassiana products will likely be most consistently effective in indoor production with high humidity conditions. There are a wide range of Cannabis pests that potentially could be killed by Beauveria bassiana (and Beauveria bassiana/pyrethrins mixtures) including aphids, thrips, whiteflies, and various caterpillars.

Beauveria bassiana containing pesticides include: Botanigard Maxx (with pyrethrins), Xpectro OD (with pyrethrins)

Horticultural Oils – (Mineral Oil/Paraffinic Oil/Petroleum Oil)

Several types of oils are available that are designed to be used on plants, collectively known as horticultural oils. These come from many sources but those with widest use are mineral oils derived from petroleum. These are highly refined to produce light oils that distill at low temperatures and that have removed compounds known to produce plant injury (e.g., aromatic hydrocarbons). They are applied as sprays (typically 1-2% dilution) and are contact insecticides without residual activity. A primary mode of action is to smother the insect by blocking the spiracles (external breathing openings).

Potential Use in Colorado Cannabis Pest Management. Horticultural oils are among the more effective treatments available that can be used to suppress twospotted spider mite. It is likely that they may also be useful in management of hemp russet mite and oils can help suppress powdery mildew. Optimal use of these products for mite suppression, and evaluation of their potential to cause plant injury when used in high temperature, high light sites, needs to be further evaluated. Caution. Oils used in combination or following applications of sulfur may cause phtotoxicity (leaf burning).

Mineral oil-type horticultural oils include: Omni Oil, Omni Supreme Spray (outdoor applications only), Bonide All Season Horticultural & Dormant Spray Oil (Concentrate and Ready-to-Spray Formulations), Leaf Life Gavicide Green 415, Mite-E-Oil, Monterey Horticultural Oil, Prescription Treatment brand Ultra-Pure Oil, SuffOil-X, Summit Year-Round Spray Oil, TriTek

Horticultural Oils – Vegetable (Canola, Cottonseed, Corn, etc.)

Several types of oils are available that are designed to be used on plants, collectively known as horticultural oils. Most widely used have been mineral oils, highly refined petroleum-based oils, but several plant derived oils are also used including cottonseed oil, canola oil, soybean oil and neem seed oil. They are applied as sprays (typically 1-2% dilution) and are contact insecticides without residual activity. A primary mode of action is to smother by blocking the spiracles (external breathing openings).

Potential Use in Colorado Cannabis Pest Management. Horticultural oils are among the more effective treatments available that can be used to suppress twospotted spider mite. It is likely that they may also be useful in management of hemp russet mite and oils can help suppress powdery mildew. Optimal use of these products for mite suppression, and evaluation of their potential to cause plant injury when used in high temperature, high light sites, needs to be further evaluated. Among the seed oils there is a range in characteristics, including ability to mix with water, evenness of flow on the plant surface, and odor. Caution. Oils used in combination or following applications of sulfur may cause phtotoxicity (leaf burning).

Vegetable oil-type horticultural oils include: #1 Pest Bully, 420 Pest Bully, Garden Guard PreFlower, Fruit Fly Bully, Wizards Brew Concentrate (castor oil), Pure 3-Way, Pure Kapow! (lemongrass and castor oil) BushDoctor Force of Nature, Eco-Mite Plus Botanical insecticide, GC-Mite, Nature-Cide All Purpose Commercial Concentrate, SaferGro Pest Out, Spider Mite Control (cottonseed oil), #1 Fungus Bully, Drench Bully, Fungus Bully (corn and castor oil), SaferGro Mildew Cure (cottonseed, corn and garlic oils), PureAg Pest Control Food Grade, Thyme Bomb (thyme and corn oil) Dr. Earth Final Stop, Organocide 3-in-1 Garden Spray (sesame oil), Root Cleaner Concentrated (soybean oil), Green Cleaner (corn and soybean oil), Captiva, Ecologic Garden Insect Killer (soybean and garlic oils, capsacin), General Hydroponics Prevasyn Insect Repellent/Insecticide (capsacin and garlic oil), SaferGro Pest-Out (Cottonseed, clove and garlic oils), Earth Tone Insect Control Concentrate (canola oil plus pyrethrins – not for commercial use), Hydro Worxx Mite & Insect Killer, Mighty, Ortho Elementals Garden Insect Killer, Spider Mite Killer, Take Down Garden Spray, (canola oil) Worry Free Garden Insectcontrol Ready-to-Use (canola oil plus pyrethrins)

Horticultural Oils – Neem (Clarified hydrophobic extract of neem oil)

Several types of oils are available that are designed to be used on plants, collectively known as horticultural oils. Most widely used have been mineral oils, highly refined petroleum-based oils, but several plant derived oils are also used including cottonseed oil, canola oil, soybean oil and neem seed oil. Neem seed oils, typically described on labels as “clarified hydrophobic extract of neem oil”, comprise the oil fraction recovered from pressed neem seeds. The primary insecticidal compounds of extracts from neem seed (particulary azadirachtin) have been removed in neem oil products. (Products that contain azadirachtin are discussed separately, above.) As with other horticultural oils, neem oils are applied as sprays (typically 1- 2% dilution) and are contact insecticides without residual activity. A primary mode of action is to smother the insect by blocking the spiracles (external breathing openings). Potential

Use in Colorado Cannabis Pest Management. Horticultural oils are among the more effective treatments available that can be used to suppress twospotted spider mite. It is likely that they may also be useful in management of hemp russet mite and oils can help suppress powdery mildew. Optimal use of these products for mite suppression, and evaluation of their potential to cause plant injury when used in high temperature, high light sites, needs to be further evaluated. Neem seed oils are often more viscous than some other horticultural oils and some have an associated odor. Caution. Oils used in combination or following applications of sulfur may cause phytotoxicity (leaf burning).

Neem seed oil containing products include: 70% Neem Oil (Monterey), Monterey Neem Oil RTU, Natural Guard Brand Neem, Neem Concentrate, Neem Oil 3n1, Rose Rx 3 in 1 Concentrate, Triact 70, Trilogy, Garden Safe Brand Neem Oil Concentrate, Safer Brand Garden Defense MultiPurpose Spray Concentrate, Schultz Garden Safe Fungicide 3 Concentrate, Bayer Advanced NATRIA Neem Oil Concentrate, Triple Action Neem Oil. Cold-pressed neem oil products include: Debug Turbo, NimBioSys, Plasma Neem Oil EC Biological Insecticide, TerraNeem EC. Neem oil/pyrethrins combinations include: Bonide Neem Oil Concentrate, Bonide Bon-Neem II Fungicide-Miticide-Insecticide Concentrate, Ferti-lome Triple Action, Fruit Tree Spray Plus, Ortho Tree & Shrub Fruit Tree Spray

Essential Oils – (Rosemary, Thyme, Clove, Cinnamon, Peppermint, Geraniol, Garlic, etc.)

Essential oils are volatile, aromatic oils extracted from plants. Many are familiar as compounds that give aroma and flavor to herbs, spices and foods. Several different types of essential oils also appear as active ingredients in insecticides, including rosemary, citronella, thyme, clove, garlic, cedar and peppermint. As most essential oils are generally considered safe, they are typically exempt from most requirements normal for pesticide registration under Section 25b.  Because of this minimal requirement for registration, many of these products make broad claims for effectiveness based on little research support. Studies on the mode of action of the essential oils as pesticides indicate many act by disrupting nerve functions in some insects. However, available information does not allow one to generalize too broadly about how these compounds act on insects and/or mites, including all of those that are associated with cannabis. It can be expected that individual essential oils (e.g., rosemary oil, garlic oil) have different modes of action and different potential to affect crop pests. Caution. Oils used in combination or following applications of sulfur may cause phytotoxicity (leaf burning).

Potential Use in Colorado Cannabis Pest Management. These products are applied as sprays to foliage. It is difficult to estimate the potential value of essential oil products for cannabis pests since they are typically blends of several oils, of varying concentrations and each may have a different spectrum of potential activity. Furthermore, there has been very little efficacy testing to support label claims, which often are broad and sometimes clearly extravagant. (These products are allowed for use under Section 25b labeling, which does not require that the manufacturer have any research support to back claims made on labels.) There is a fair body of research to support the potential effectiveness of some essential oils (e.g., rosemary oil, thyme oil) to control some pests that occur on cannabis, particularly spider mites. Potential phytotoxicity has occurred with some essential oils (e.g., cinnamon) on some crops. Phytotoxicity evaluations are lacking on cannabis.

Essential oil containing products include: Spider Mite Eggsterminator

Sulfur

Elemental sulfur is one of the oldest pesticides in use. It is usually formulated as a flowable formulation for sprays of foliage. Sulfur has activity against many types of pests including fungi, some mites and some insects, but is usually sold for control of foliar fungi such as powdery mildew.

Potential Use in Colorado Cannabis Pest Management. Sulfur is labeled for use in control of certain foliar fungi, such as powdery mildew. It may have some suppressive effect on spider mites. Presently the only sulfur containing product allow for use on Cannabis is limited to home growing operations, not for commercial production. CAUTION. The use of sulfur on a crop can cause phytotoxicity if oils are used, either in co-application or within 2-3 weeks of a sulfur application.

Sulfur containing products include: Safer Brand 3-in-1 Garden Spray II, Safer Brand Concentrate II, Hi-Yield Snake Eyes Dusting Wettable Sulfur, Safer Brand Garden Fungicide for Flowers, Fruit, and Vegetables; Safer Brand Garden Fungicide II for Flowers, Fruits, and Vegetables; Bonide Eight Insect Control Home & Garden Ready to Use, Earth-tone 3n1 Disease Control.

Pyrethrins

Pyrethrins are naturally derived insecticides extracted from the flowers of the pyrethrum daisy Tanacetum (=Chrysanthemum) cinerariifolium. This insecticide has a very long history of use and has activity against many insects. Advantages useful for control of some insects include fast ‘knock down’ activity, repellency, and very short residual effects. Pryethrins are most widely used for control of various flies (including mosquitoes) and caterpillars. Pyrethrins products are often formulated with piperonyl butoxide, which acts as a synergist that can greatly increase the activity of pyrethrins. Pyrethrins are also sometimes combined with various oils (e.g., canola, neem); the oils may provide control of some species (e.g., mites) that are not controlled by pyrethrins.

Potential Use in Colorado Cannabis Pest Management. Pyrethrins appear to have little potential value in pest management of the pests found in Cannabis. Claims for use in control of spider mites are very questionable and it is unlikely to have any value for control of this pest on the crop.

Pyrethrins products include: Azera Gardening & Insecticide, Earth-tone Insect Control, Take Down Garden Spray, WorryFree brand Garden Insect Control (with canola oil), Ferti-lome Triple Action, Fruit Tree Spray Plus (with neem oil), Bonide Bon-Neem II Fungicide-MiticideInsecticide, Ortho Tree & Shrub Fruit Tree Spray, Bayer Pyrenone Crop Spray, Prescription Treatment Brand Pyrethrum TR Micro Total Release Insecticide, Pyronyl Crop Spray, TyGRO Insect Fogger I, Safer Brand Yard & Garden Insect Killer II, Bug Buster-O, Evergreen Pyrethrum Concentrate, Lynx EC 1.4, Lynx EC 5.0, Pyganic Crop Protection EC 1.4 II, Pyganic Crop Protection EC 5.0 II, PyGanic Gardening, Pyganic Specialty, Tersus Insecticide, Botanigard Maxx (with Beauveria bassiana), Xpectro OD (with Beauveria bassiana), Hydro Worxx Mite & Insect Killer, Mighty, Ortho Elementals Garden Insect Killer, Shield-All Plus Broad Spectrum Insecticide, Fungicide, Miticide; Evergreen Crop Protection EC 60-6, Evergreen Pro 60-6, PestXpert Pyrethrum PBO Plus, Prescription Treatment brand Pyreth-It Formula 2, Pyrethrum TR Total Release Insecticide, Ferti-lome Fruit Tree Spray, Bonide Eight Insect Control Home & Garden Ready to Use, Earth-tone 3n1 Disease Control (with sulfur).

Potassium Sorbate

Potassium sorbate is a common food additive used primarily to suppress growth of molds.

Potential Use in Colorado Cannabis Pest Management. There is very little – if any – data to support label claims of potassium sorbate to be able to effectively control mites or insects on growing crops, including those that affect Cannabis. Given the primary use of this product in food preservation it may have some value in suppression post-harvest fungi, but this is neither been tested nor is among label claims.