by Nebula Haze
Stop Caterpillars From Attacking Your Cannabis!
Caterpillars!!! Argh!!! Sometimes the first sign of caterpillars / worms / cabbage loopers is just seeing chunks of your leaves missing. You may also see clumps of black/brown “dirt” on your leaves, which is caterpillar poop. Lastly, you may actually catch a caterpillar munching on your leaves. It can be angering to catch them in the act.
Caterpillars are one of the most common cannabis pests when growing weed outdoors. Use BT Caterpillar spray (works best if you apply it with a mister) as a safe and effective way to eradicate them for good.
Zebra caterpillar on a cannabis leaf, picture by Whitney Cranshaw of Colorado State University
Saltmarsh caterpillar on cannabis leaf, picture by Whitney Cranshaw of Colorado State University
Another saltmarsh caterpillar on a marijuana leaf, picture by Whitney Cranshaw of Colorado State University (thank you!!!)
You’ll see chunks of your leaves missing from the caterpillars devouring your leaves
caterpillar leaf damage pic by molpes
Caterpillar Droppings on Leaves
You Actually See Caterpillars, Inchworms or Cabbage Loopers
caterpillar pic by Waterproof
Caterpillar “BT” Spray (safe biological insecticide)
This biological insecticide contains the bacillus thuringiensis (BT) bacteria which kills larva and prevents caterpillars from being able to eat. This is one of the most effective ways to kill caterpillars, and won’t hurt most beneficial insects. As a bonus, it also kills other cannabis pests like fungus gnats, worms and moths. Apply a caterpillar BT spray as soon as you see leaf damage, caterpillars or caterpillar poop. BT sprays work best on small caterpillars that are actively eating your leaves. Repeat every week for as long as you’re still seeing caterpillars, though you can give BT more often if there’s a heavy infestation. Make sure to thoroughly mist both the tops and bottoms of leaves, and apply again after a heavy rain (since that will wash the BT away). Since BT is harmless to humans, you can use BT products up to the day of harvest! One thing to keep in mind is BT spray almost instantly stops caterpillars from being able to eat, but doesn’t kill them directly. So although you may see the caterpillars alive and apparently unharmed after spraying, the BT is still doing its dirty work.
Recommended: Monterey BT Spray + a mister
(though any caterpillar BT product will work!)
Spinosad Products (safe & organic)
Although not as effective against caterpillars as a BT product, Spinosad can be a good choice, especially if your plants are also suffering from other insects like aphids, spider mites, thrips or white flies since this will attack all of them at once. Spinosad products are organic and completely harmless to pets, children, and plants. Unlike many insecticides, you can spray properly diluted spinosad heavily on leaves and roots with basically no negative effects. Spinosad products can be used directly to kill caterpillars on contact, but can also be used when watering plants to systematically kill caterpillars via the soil.Spinosad is an organic insecticide made from the fermentation of a specific soil bacteria (actinomycete Saccharopolyspora spinosa) and kills caterpillars via ingestion or contact by effecting the insect nervous system. Spinosad can be a good choice for organic and outdoor growers, because it is very toxic to caterpillars, but is less toxic to many beneficial insects. Note: Most spinosad products are effective for only about 24 hours after being mixed with water, so only mix as much as you will need per application. Anything left over will be a waste. WARNING: Commercial growers click here!
Recommended: Monterey Garden Insect Spray with Spinosad (not for commercial growers)
Avoid butterflies and moths! Although these beautiful creatures look great resting on your cannabis plants, they lay eggs that hatch into caterpillars. Don’t let them hang around your garden.
More Cannabis Pests, Bugs & Viruses