Getting Rid of Caterpillars on Cannabis Plants

Caterpillars on pot plants can be a nightmare for cannabis growers. These voracious pests chew through leaves, stems, and even buds, causing serious damage. Many growers hesitate to take action for caterpillar damage due to concerns about pesticide safety; however, effective and safe solutions are available. 

Understanding why caterpillars are attracted to cannabis plants throughout their life cycle is the first step in preventing infestations. In this article, we’ll cover different types of caterpillars that threaten cannabis, chemical and biological control methods, and how to deal with caterpillars during the flowering stage and drying stage.

Types of caterpillars that eat cannabis

Several caterpillar species feed on cannabis plants, with variations depending on the region and environmental conditions. Identifying the specific type of caterpillar infesting your garden can help tailor your pest control approach. Common types include:

• Corn Earworm (Helicoverpa zea) – A major threat to cannabis, these larvae burrow into buds, causing rot and mold issues.
• Cabbage Looper (Trichoplusia ni) – Feeds on cannabis leaves, reducing photosynthesis and plant vigor.
• Cutworms (Agrotis spp.) – Nocturnal feeders that chew through stems, causing plant collapse.
• Armyworms (Spodoptera spp.) – Highly destructive, they can strip cannabis plants of foliage overnight.
• Hemp Borer (Grapholita delineana) – A significant pest of cannabis, the hemp borer burrows into stems and buds, leading to plant weakening and increased susceptibility to mold and disease.
• Imported Cabbageworm (Pieris rapae) – Though typically associated with Brassicaceae crops, these larvae have been observed feeding on cannabis buds, leading to bud rot.

Environmental factors such as surrounding vegetation and climate influence which caterpillars are present. Those growing cannabis near agricultural fields or wild vegetation may experience more pest pressure. This is specifically true for the imported cabbage moth.

How to Get Rid of Caterpillars on Cannabis

The most effective way to eliminate cannabis caterpillars is to address them from multiple angles. There are three pillars to Integrated Pest Management: Cultural, Biological, and Chemical, and gardeners should use all three when treating any pest.

Cultural Controls to Manage Caterpillars

Cultural controls are the measures you take as a gardener to prevent or treat weed caterpillar infestations. This includes practices such as:

• Observation: If you see butterflies or moths in your garden, observe where they land and feed. Identify the species and research what they eat and where they lay their eggs.
• Inspection: Regularly inspect your plants for dead or diseased plant material and other signs of caterpillars. Cleanliness is key to preventing infestations. 
• Hand removal: Physically remove any caterpillars you find. Throw them far away from your garden or feed them to your chickens. If you don’t have chickens, maybe this is your sign to get some.

Biological Controls to Manage Caterpillars

Biology controls are those that utilize living organisms as a means of pest treatment or prevention. Biological controls provide an eco-friendly alternative to chemical pesticides. Some effective methods include:

• Companion Planting: Plants like Lemon Balm deter cabbage moths, while others, such as buckwheat, can attract beneficial insects like parasitic wasps.
• Beneficial Insects: Parasitic wasps (Trichogramma spp.) lay eggs inside caterpillars, preventing them from maturing. Green lacewings and assassin bugs also kill caterpillars.
• Predatory Nematodes: Microscopic worms that invade and kill caterpillars in the soil.
• Birds and Bats: Encouraging natural predators can damage caterpillar populations in helpful ways. Consider bird feeders, chickens, or companion planting sunflowers. 

Chemicals to manage caterpillars

These products are made from soil-dwelling bacteria, fungi, and plants. Chemical insecticides can be effective, but caution is needed when applying them to cannabis plants, especially during flowering. Some commonly used options include:

• Bacillus thuringiensis (BT-k): A naturally occurring gram-positive bacterium that produces toxins targeting caterpillars.
• Beauvaria bassiana: A naturally occurring fungal mycoinsecticide infects caterpillars, disrupting their activities and ultimately leading to their demise.
• Spinosad: Derived from soil bacteria, this insecticide is effective against caterpillars but must be used with caution. This product kills both beneficial and pest insect species, so use it sparingly.
• Neem Oil: Neem oil disrupts caterpillar feeding and development without harming beneficial insects. It should not be used during the flowering phase of growth as it has a very strong smell.

Growers should follow label directions and avoid using chemical controls close to harvest to prevent residue contamination.

Caterpillars during flowering

During the flowering phase of growth, caterpillars can devastate cannabis plants by burrowing into buds and leaving waste behind.

Caterpillar droppings.

What is the Best Pest Control for Caterpillars?

• Regular inspections and handpicking caterpillars.
• Applying BT consistently if you see any caterpillars.
• Support companion planting that encourages natural predatory insects to attack caterpillars.

Caterpillars during drying

Caterpillars present during the drying phase can lead to bud rot and mold development. Check out these solutions to limit crop loss:

Best Solutions:

• Thoroughly inspect buds before drying.
• Use a controlled drying environment with proper humidity levels (50-60%).
• Shake or gently tap dried buds to remove any hidden caterpillars.

Is BT safe to use on cannabis plants?

BT is a naturally occurring soil bacterium producing crystal proteins (Cry toxins) that target caterpillar larvae while being harmless to humans, pets, and beneficial insects. The half-life of Bt toxin on plants is typically between one and four days; this means it is safe to use up until the week prior to harvest.

There are two different types of BT, one targets caterpillars (BT-k), the other targets fungus gnats and mosquitoes (BT-i). Make sure you are using the correct type. The disadvantages of using BT are that it washes off easily, making its reapplication necessary. 

Another issue to be aware of is that it kills all caterpillars and should therefore be used with caution, as many of our pollinators, such as the monarch butterfly, are under threat of becoming endangered.

You can help our pollinators by planting a variety of flowering species around the perimeter of your cannabis garden. This will provide nectar for moths and butterflies, as well as attract beneficial insects that feed on caterpillars. Try sunflowers, zinnias, native milkweed, buckwheat, and sweet alyssum to attract a diverse crowd of crop defenders and butterflies alike. 

Is Spinosad safe to use on cannabis plants?

Spinosad is another biological insecticide that is effective against caterpillars but should be used cautiously. Because it is a broad-spectrum insecticide, it can harm both beneficial and pest insects.