Common Cannabis Pests and How to Mind Them
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Like any crop, cannabis can often find itself at the mercy of ravenous animals, desperate for a field feast. So, whether you’re growing indoors or outdoors, knowing your plant’s enemies is the first step in protecting them. From crickets to caterpillars, moles to mites, this article outlines cannabis’ top predators, their tell-tale signs, and how to best remove them.
As cannabis is intended for human consumption, it is important to use food-grade materials or approved general recognized as safe (GRAS) insecticides and chemicals in the garden. Avoid application of hazardous materials and make all effort to not spray harsh products on flowers. Soaps and oils may leave unpleasant flavors or odors on your crop, making them unappealing for use.
Ants on cannabis plants can be bad news. These well-known insects damage the root system, negatively affecting the overall plant yield. Even worse, an ant invasion usually precedes an aphid infestation. If there is an aphid outbreak in tandem with an ant infestation, eradicate the ants quickly as they can move aphids to safety and protect them from beneficial insects.
Look for ant trails, mounds, or hills. While aphids feed on the cannabis leaves, ants often harvest the aphid’s honeydew for nutrients. Therefore, ants would always protect the aphids, allowing the pest colony to multiply.
Insecticidal soaps containing peppermint or orange oil sprayed on unflowering plants. Saturate colony mound and tunnel with mineral and/or botanical oils. Clean up any undecomposed compost or foodstuffs from the garden that may be attracting the colony. Ant hills can be flooded with water to encourage the colony to relocate. Cinnamon is known to be a famous ant treatment for people with small gardens. It works as a repellent and an exterminator since the insects are repulsed and killed by it. Growers should sprinkle or water it onto the soil where they are nesting. In general, however, there aren’t a lot of treatment measurements that can completely get rid of ants. Gardeners can encourage their natural predators such as frogs and slow worms to come to your garden. Finally, growers can grease your trees and stems of plants, or place them in a moat of water. Ants won’t be able to cross the water or the greased parts.
Birds are an outdoor cannabis pest, who might help you out by eating insects or just ruin your future harvest by stealing seeds or defecating on the crop.
Birds are definitely easier pests to spot. You need to check on your crops regularly if there have been any bird-plant interactions or seeds disappearing.
A classic solution is to distract the bird pests by placing scarecrows or shiny objects (e.g. cans) near your crop. Owl decoys, especially ones with rotating heads, can effectively scare off birds. It is key to move them around the garden every two to three days. Another distraction is a bird feeder situated on the property line. Alternatively, use a lightweight net or PVC cover to create a barrier. Shade cloth and light depravation materials covering flowering plants during daylight hours may also reduce bird damage.
Crickets and grasshoppers
These noisy insects are common cannabis pests that live among the branches and feed intensively on leaves, stems, and flowers. Grasshoppers and crickets can be difficult to kill because they are highly mobile and populations fluctuate yearly.
Crickets and grasshoppers are outdoor cannabis pests that can be identified by the sounds they make and their noticeable feeding marks on the plant leaves. Surveying fields for presence of grasshoppers and crickets helps inform pest management strategies. Sweep net sampling, bait trips, and other methods that allow for determination of insect density should be used.
Pest controls, can attack the cannabis pest directly and kill them. Additionally, treatments with neem oil, insecticidal soaps, and Bacillus thuringiensis-based products are also suggested when dealing with grasshopper and cricket invasion on cannabis plants. Bacillus thuringiensis (Bt) is a bacterium that kills caterpillars, grasshoppers, and other chewing insects. Apply Bt to soil or base of newly planted cannabis early in the season to control larval populations. Border treatments around the field with more aggressive chemicals may be sufficient to control hopper populations. Tilling soil in the spring may destroy egg pods by mechanical damage and exposure to parasites, weather, or predators.
Gophers and moles
If growing cannabis in North America, these toothy rodents can be an exhausting underground menace. They feed mainly on the crowns and roots of plants, and populations can increase rapidly in a good year. Gopher and mole holes can damage irrigation lines and create uneven water distribution.
Rodents are the nightmare of every outdoor horticulture farmer because they are hard to identify unless they are spotted in action or their traces and earth holes are noticed. Look for soil mounds over tunnel openings or raised soil around the field. Look for stressed plants as some activity is not visible aboveground.
To deal with gophers and moles, try spraying castor oil and garlic water mixture over the garden soil, which should make the pests migrate. Alternative organic pest control solutions are using hardware cloth, setting pinch traps, or even simply getting a cat. Controlling cover crops with landscape fabric reduces food sources. Flood irrigation and deep tilling while fields are fallow will destroy burrow systems and slow reproductive rates. Limit use of anticoagulant baits as these can harm predators such as birds, snakes, and mammals. Burrow fumigants are another option in late winter or early spring after the cannabis crop has been harvested.
Just like the name implies leaf miners feed on plant sap and lay eggs within leaf tissues. Larvae hatch within the leaves, feeding between the upper and lower leaf surfaces, creating distinctive winding tunnels or mines.
After inflicting their initial damage on the plants, the leaf miner larvae eat the tissue and leaves, leaving long white traces on the cannabis leaves. Those lines are the warning sign you need to look for in order to identify the unwelcome pest in time. Heavy leaf miner infestations can cause leaf drop, stunted growth, and yield reduction.
Luckily, the adult leaf miners can be stopped from laying more eggs. A savvy grower should place adhesive strips near the crops. But to deal with the larvae, one can treat the plant with insecticides such as azadirachtin, neem, or horticultural oils. Parasitoid wasps and generalist predators like lacewing larvae will feed on leaf miners.
Spider mites damage the cannabis plant by sucking the sap from its leaves, killing the crop in a tight timeframe. Mite populations can quickly become unmanageable and resistant to pesticide applications.
To notice traces of spider mites on cannabis plants, you need to look for tiny white or yellow spots on leaves, known as stippling. Visual confirmation of spider mites feeding and moving on the leaves can be observed with a hand lens (magnifying glass) or by the naked eye. Webbing, bleached or bronzed leaves, or leaf drop indicate a severe infestation.
Spider mites thrive in dry areas and multiply in high temperatures. Once spotted, the damaged leaves need to be treated by spraying a mixture of alcohol and water on the problematic areas. Other products that could help are insecticidal soaps, neem, horticultural oil, and ecotenona. Spider mites are known to dislike applications of rosemary or other botanical oils. High-pressure water sprays can dislodge mites and destroy their protective webbing while increasing relative humidity and decreasing temperatures around plants. If there is an outbreak on flowering plants, carefully consider intense water applications and potential bud rot issues. Biological control employing predatory mites or other beneficial insects can help with light infestations or for prevention. Beneficial species will not be able to eradicate a spider mite infestation.
Caterpillars are cannabis pests who need to form a chrysalis to develop into their adult form, so they feed on plants at a fast rate.
Yellow or translucent eggs, chewing marks, ragged holes, and black droppings on the leaf surface are all major signs which should alarm any grower of a caterpillar invasion.
Luckily, caterpillars on cannabis plants can easily be spotted and removed by hand. Alternative treatments include applying pepper and garlic insecticide, as well as introducing Trichogramma wasps or spined soldier bugs to the plantation. Bt can also be applied to the soil or at the base of the plants early in the season to limit caterpillar infestations. Azadirachtin, neem oil, and other insecticidal oils can help as well. Insect barrier fabrics can also be used if expecting a severe outbreak.
A fast, tiny insect, thrips can be hard to spot and treat.
Sticky strips could be used to identify the thrips’ invasion, but another way to determine their presence is to look for brittle leaves and silver markings on a plant’s surface. A leaf tap test is also useful in determining their presence.
Spraying with potassium soap or neem oil could be extremely helpful unless the flowering process has already started. If this is the case, then alternative cannabis pest control measures need to be taken into consideration – including wasps or insidious flower bugs. A thrip’s life cycle requires a comprehensive pest management approach. Adults lay eggs in the leaves, larva drop to the soil to pupate, then emerge as winged adults. Treating soil with predatory nematodes and soil mites is highly effective to reduce populations. Thrip populations can easily become pesticide-resistant, so use multiple chemistries at label-listed application rates to avoid this possibility.
Whiteflies are a common pest that weakens cannabis plants by sucking the sap from their leaves.
The obvious evidence of whitefly infestation on cannabis leaves is the presence of tiny flies every time the plants are shaken. Other symptoms of invasion include yellowed leaves with white powder on their underside. Whiteflies tend to congregate on undersides of leaves.
The stubborn whiteflies are tough to get rid of. They need to be treated persistently with various methods like planting repellent crops (e.g. basil), strategically placing yellow sticky strips, or spraying with neem oil or potassium soap. Parasitoid wasps, lacewing larvae, pirate bugs, and others can be effective in reducing whitefly populations. Reflective mulches and weed control can deter whiteflies.
Aphids are extremely fast at spreading and reproducing. Like other cannabis insect pests, they feed on the leaf sap.
If you notice dry yellowish leaves, honeydew and colonies under stems and leaves, then you are probably dealing with an aphid invasion.
Insecticidal soaps, azadirachtin, and neem or horticultural oils are effective in treating aphids. Introducing plant-friendly insects to feed on aphids is also a solution (e.g. lacewing larvae, parasitic wasps, lady bird beetles). Root aphid populations can be managed with azadirachtin and pyrethrin drenches.
Another nemesis of marijuana growers, cochineals reproduce at a rapid rate and their droppings decay plant material and lead to cannabis leaf problems.
These common cannabis pests are white or brown in color with a white fluff cover. Tiny and hard to detect, they initially appear on the stems and then infest the whole cannabis plant.
Even though cochineals are resistant to some insecticides, removing them by treating the leaves with a mixture of alcohol and water (50/50) would be useful to eradicate this pest. All severely affected parts of the plant should be removed.
Roundworms (nematodes) have 25,000 registered species, half of which are plant damaging parasites, while the other half are actually beneficial for the cannabis crop.
Symptoms of nematodes on a cannabis plant include chlorotic leaves, lack of vigor, slowed growth, and wilt.
The treatment against nematodes on cannabis plants is applying products like nematicides, Trichonema Prot-L, neem oil, and laotta. You can also ensure roundworm-free plantations by regularly changing the substrate.
Slugs and snails
Snails and slugs are common pest of any crop, cannabis included.
Spotting them is relatively easy since they leave shiny trails of transparent mucus.
The best cannabis pest control option for slug and snails is removing them manually at night when they are most active. Alternative treatments include building a barrier around the crop, placing baits and lures (e.g. mix of jam and beer), and using the predatory slug Ruminia decollate.
Broad mites and russet mites
Broad mites (Polyphagotarsonemus latus) and russet mites (Aculops species) are miniscule mites, too small to see with the naked eye, that damage many crops. They are often detected after a severe infestation has taken hold of the crop.
Typical symptoms mimic herbicide damage. Leaves turn small, stunted, and they sometimes curl downward and inward.
The pests can be controlled via applications of selected miticides labeled for broad or russet mites. Many miticides that work on other mites, such as spider mites, make little impact on reducing these pests. Applications of micronized sulfur on non-flowering cannabis plants can help reduce the populations. Micronized sulfur cannot be applied in conjunction with agricultural oils as it can cause severe phytotoxicity. Sulfur applications will need to continue on non-flowering plants until all flowering plants infested with broad or russet mites have been removed from the field or harvested. These mites can overwinter in the soil or on porous surfaces, so clean and sterilize areas to the best of your ability.
Cannabis pests’ identification and extermination is crucial. It is essential for any grower to be able to identify a pest and react fast to protect their greenery and ensure the well-being of their plantation.
Update: This article was updated on June 29, 2022, to include information on pest treatments.