Dealing with Insects on Cannabis Plants

Understanding and managing pests is crucial for healthy cannabis growth. This guide will help you identify common cannabis plant pests, understand their impact, and learn effective prevention and control methods for infected plants.

In the world of gardening, pests are often a nuisance that can range from annoying to downright destructive. Luckily, there are ways to deal with pests that keep your cannabis clean and safe for consumption. No one wants to find bugs on marijuana plants, but spraying chemicals is much more dangerous compared to bugs in weed nugs. 

This is especially important when marijuana is being used as medicine for diseases like cancer, that require large doses, often in concentrated forms. As cannabis becomes concentrated, so do the chemicals that have been applied to it. That’s why it is important to use an integrated pest management plan that targets marijuana pests in various ways known to be harmless to humans.

What is IPM?

Integrated Pest Management, also known as IPM, is a method of dealing with pests in a sustainable and holistic manner. There are three methods of IPM: Cultural, Biological, and Chemical. These practices will vary depending on whether your garden is indoors vs outdoors.

Cultural IPM

Cultural IPM are the practices you can implement to prevent pests from getting into your garden, and physical practices you can implement once pests have arrived. They include changing clothing before entering your garden if you’ve been inside someone else’s, cleaning and sterilizing your tools with bleach in between uses, or regularly scouting for pests and mechanically removing them and killing them as you find them. Proper sanitation procedures can be used to prevent and eliminate almost all pests, both indoors and outdoors.

Cannabis Pest Identification and Prevention

By creating good habits, you can prevent infestations and maintain healthy populations of pests outdoors. If you have bugs on your weed plants, the first thing you need to do is properly identify them before making any effort to treat them. Use sticky fly traps and magnification to visually identify what types of bugs are on your pot plants. Many treatments are pest-specific, especially when using biologicals.

Biological IPM

Biological IPM, as the name suggests, uses other living organisms to help prevent or treat pests. These practices can range from companion planting different species of plants that attract beneficial insects outdoors to purchasing beneficial insects for use indoors. Other techniques that are incredibly efficient are using a variety of microorganisms to treat pests. Different microbes can be used to treat different pests.

Companion planting in the greenhouse.

Predator Insects

When growing outdoors, you can incorporate a wide range of plant species that attract predatory insects into your garden. Yarrow, buckwheat, sweet alyssum, lemon balm, sunflowers, sill, oregano, and cilantro are just a few examples of plants that can be incorporated into your cannabis garden that will attract predatory insects. 

The more diversity in plant species, the more diversity there is in insect species. Indoor gardeners can purchase predatory insects like ladybugs, assassin bugs, green lacewings, and praying mantis, but that may not be the best route as they will consume pests, poop, and die in your indoor space.

Microbial Biocontrols

Microbial biocontrols utilize microorganisms to treat pests. There is a wide range of bacteria, fungi, nematodes, and protozoa that kill weed plant bugs using different modes of action. For example, Beauvaria bassiana, a type of entomopathogenic fungi, is more of a wide-range treatment, while Bacillus thuringiensis, a type of bacteria, can be used to either kill fungus gnats or caterpillars depending on the subspecies. It is important to make sure you have properly identified your pest before spending money on these types of products. 

Chemical IPM

This pillar of IPM is the one you want to use the least, it is incredibly efficient at knocking back pot pests but can also be detrimental to beneficial bugs on cannabis plants and have lasting effects on ecosystems when applied outdoors. Certain organic chemicals can even become systemic within plant tissue and show up in your flower or concentrate. Consuming these chemicals through combustion and inhalation or ingestion through edibles may have detrimental side effects. 

Certain chemical pesticides, such as pyrethrins are safer to use indoors than outside. There is no risk of harming beneficial bugs on weed plants indoors when using these types of broad-range pesticides. Do not use chemical pesticides when your plants are in flower.

12 Common Cannabis Pests

In the following section, we will discuss the most common cannabis pests and how to address them culturally and biologically. Most chemical pesticides should be avoided, but there are some, such as spinosad, neem, horticultural oil, insecticidal soaps, and pyrethrins, that are broad-range and work on most weed pests. Always read the label and apply chemicals with caution. 

Aphids

Aphids are small, pear-shaped bugs that come in various colors, including green, black, and yellow. They feed on the sap of cannabis plants and can cause yellowing of leaves if left untreated. It’s easy to spot aphids on the underside of leaves and the stems.

Aphid on cannabis plant under 1x magnification.

These buds can attract ants that feed on the honeydew excreted by the aphids. Aphids are born pregnant and can lay 4-12 young per day, so treating them as soon as you see them is important.

 Cultural Practices

• Avoid over-fertilization, particularly of nitrogen, as aphids are attracted to succulent new growth. Refrain from topping plants if aphids are present.
• Use water sprays to knock aphids off plants and wash away honeydew. Spray in the early morning to prevent fungal pathogens.
• Plant pungent strains like All Gas OG to naturally deter aphids, which are known for being attracted to sweeter strains. 

Biological Controls

• Introduce or attract predatory insects like parasitic wasps, lady beetles, lacewing larvae, and hoverfly larvae.
• Use entomopathogenic fungi such as Isaria fumosorosea, found in products like No Fly, especially in humid environments.

Chemical Controls

• Apply gentle sprays of isopropyl alcohol, unscented castile soap, and water to coat and dehydrate aphids.
• Utilize organic options like neem oil, which act as insect growth regulators and work well with entomopathogenic fungi to control aphids and other pests

Caterpillar on cannabis plant.

Caterpillars

Caterpillars are larvae of butterflies and moths that can cause significant damage by chewing through leaves and buds. This feeding activity can result in stunted growth, reduced yields, and increased vulnerability to marijuana plant diseases like botrytis.

Cultural Practices

• Remove caterpillars from leaf surfaces by hand if you see them with the naked eye. Early morning is the best time to inspect the grow space.
• Encourage a diverse garden with flowering plants that attract predatory pot plant insects and birds.

Caterpillar feces.

Biological Controls

• Introduce or attract natural predators like birds, parasitic wasps, and predatory beetles.
• Use Bacillus thuringiensis (Bt), a natural soil bacterium, which targets caterpillars specifically.

Chemical Controls

• Use organic pesticides such as spinosad for severe infestations.

Earwigs

Earwigs are nocturnal insects on weed plants that chew on leaves and stems, often hiding during the day in moist, dark areas. While not commonly associated with weed, their feeding can lead to irregular holes in leaves and can compromise plant health in young seedlings.

Cultural Practices

• Reduce moisture levels and remove infected plant debris to eliminate earwig hiding places.
• Use coarse ground diatomaceous earth around the base of plants as a physical barrier.
• Set up damp rolled newspaper traps to capture earwigs overnight.

Biological Controls

• Attract natural predators such as toads and birds.

Chemical Controls

• Use bait traps with boric acid to control earwig populations.

Fungus Gnats

Fungus Gnats are small, dark flies that lay their eggs in moist soil. The larvae feed on organic matter and roots, causing damage to root systems that can stunt plant growth and increase susceptibility to root rot and other cannabis plant diseases.

Cultural Practices

• Allow the soil to dry out between waterings to disrupt the gnat life cycle.
• Improve soil drainage and avoid overwatering.
• Apply sticky traps to catch adult gnats and monitor the population.

Biological Controls

•  Introduce beneficial nematodes that target gnat larvae.
•  Use Bacillus thuringiensis (Bt) as a soil drench to kill larvae.

Chemical Controls

• Neem, Pyrethrins, and Spinosad can be used to kill both larvae and adult fungus gnats. Root drench these products to target the larva stage and eliminate risks associated with ingesting by spraying on the plant.

Grasshoppers

Grasshoppers are large, jumping insects that chew on leaves, often causing significant defoliation. Their feeding can severely reduce plant vigor and yield.

Cultural Practices

• Maintain healthy soil and plant diversity to discourage infestations. Planting herbs like cilantro, calendula, or artemisia can repel grasshoppers.
• Handpick grasshoppers and destroy them or feed them to backyard chickens.

Biological Controls

• Attract natural predators such as birds, frogs, and spiders.
• Use microbial insecticides like Nosema locustae, which target grasshoppers. Nosema locustae is a protozoan belonging to the phylum Microsporidia, a group of spore-forming unicellular parasites. It primarily infects grasshoppers and some species of crickets, making it highly specific and reducing the risk to non-target organisms.

Chemical Controls

• Apply neem oil or spray insecticidal soaps to affected plants during the vegetative stage.

Hemp Borers

Hemp Borers are larvae that tunnel into the stems and buds of cannabis plants, causing structural damage and reducing yields. They can also introduce pathogens that lead to cannabis diseases and pests.

Cultural Practices

• Remove and destroy affected plant parts to prevent further spread.
• Monitor plants regularly for signs of infestation.

Biological Controls

• Introduce trichogrammatid wasps and assassin bugs that target hemp borer larvae.
• Use Bacillus thuringiensis (Bt) to kill larvae within the plant.

Chemical Controls

• Apply neem oil to prevent egg laying.
• Use organic insecticides like Spinosad or pyrethrins for severe infestations.

Leafhoppers

Leafhoppers are small, wedge-shaped insects that suck sap from cannabis leaves, causing them to yellow and curl. Their feeding can transmit plant pathogens, such as curly beet virus, and reduce overall plant vigor.

Cultural Practices

• Maintain plant health through proper watering and fertilization.

Biological Controls

• Introduce or attract natural predators such as lady beetles and lacewings.
• Use entomopathogenic fungi like Beauveria bassiana to control leafhopper populations.

Chemical Controls

• Apply insecticidal soaps or neem oil to infested plants.
• Use organic pesticides like pyrethrins for severe infestations.

Pill Bugs 

Pill Bugs, also known as rollie-pollies, are typically considered beneficial outdoors as they cycle nutrients by breaking down decaying organic matter. But indoors, their population, left unchecked, these cannabis bugs explode and devour young shoots and roots, causing stunted growth.

Cultural Practices

• Do not introduce pill bugs into your indoor garden.
• Remove plant debris and avoid over-mulching outdoors if they become a problem.

Biological Controls

• Introduce predatory beetles that feed on pill bugs.
• Use ground beetles and other natural predators to control populations.

Chemical Controls

• Apply coarse ground diatomaceous earth around plants as a physical barrier.

Root Aphids

Root Aphids are small, sap-sucking insects that attack the roots of cannabis plants, causing yellowing leaves, stunted growth, and reduced vigor. These weed bugs can spread quickly and are difficult to detect without many early signs.

Cultural Practices

• Avoid overwatering and improve soil drainage to prevent root aphid infestations.
• Source soil from clean manufacturers, commercial soils may harbor root aphids.

Biological Controls

• Introduce beneficial nematodes that target root aphids.
• Use entomopathogenic fungi like Beauveria bassiana to control aphid populations.

Chemical Controls

• Apply insecticidal soaps or neem oil as a soil drench.
• Use organic insecticides like pyrethrins for severe infestations.

Russet Mites

Russet Mites are microscopic pot plant pests that cause leaf curling, bronzing, and russeting, leading to stunted growth and reduced yields. They are difficult to see without magnification.

Cultural Practices

• Avoid over-fertilization and excessive pruning, which can encourage mite infestations.

Biological Controls

• Introduce predatory mites like Phytoseiulus persimilis to control russet mites.
• Use entomopathogenic fungi such as Beauveria bassiana.

Chemical Controls

• Apply sulfur sprays to affected plants during the vegetative phase.
• Apply horticultural oil during the flowering phase.

Spider Mites

Spider Mites are tiny pests that create webs and cause yellowing and speckling on leaves. Heavy infestations can lead to significant plant damage.

Cultural Practices

• Plant hedge rows around outdoor garden space to create a physical barrier that limits movement to control spider mites.

Biological Controls

• Introduce predatory mites such as Phytoseiulus persimilis.
• Place companion plants like sweet alyssum and buckwheat to attract insect predators that feed on spider mites.
• Use entomopathogenic fungi like Beauveria bassiana to control populations.

Chemical Controls

• Apply horticultural oil and soap.

Thrips

Thrips are tiny, slender insects that scrape and feed on plant tissues, causing silver streaks on leaves and stunted growth.

Cultural Practices

• Use blue sticky traps to monitor and catch adult thrips.

Biological Controls

• Introduce or attract predatory insects like minute pirate bugs and lacewings.
• Use entomopathogenic fungi like Beauveria bassiana.

Chemical Controls

• Apply insecticidal soaps or neem oil to affected plants.
• Use organic insecticides like spinosad for severe infestations.

Conclusion

Effective pest management is essential for maintaining healthy cannabis plants and ensuring a bountiful harvest. By identifying common pests, implementing preventive measures, and using a combination of organic and chemical control methods, growers can protect their crops from the damaging effects of insects and weed plant diseases.

By following this guide, you can keep your cannabis plants free from pests, ensuring robust growth and high-quality yields. Remember, a proactive approach to pest management is always better than a reactive one, so regular monitoring and maintenance are key to a successful cannabis grow.