worms in weed plants

Caterpillars & Inchworms

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 so angering to catch them in the act!

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

Proven Caterpillar Remedies

  • 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.
  • 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 waste.
  • 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!

Learn how to identify and get rid of caterpillars (and other little worms) and prevent them from ever attacking your cannabis again!

Getting Rid of Caterpillar Infestations

Inicio » Crop articles » Getting Rid of Caterpillar Infestations

Getting rid of caterpillar infestations in cannabis grows is a relatively easy task if you catch them early enough; once those caterpillars have grown into mini snakes from hell, however, it isn’t such an easy task.

Caterpillars don’t just come out of nowhere; those little inoffensive grey moths aren’t as inoffensive as you once thought, as they lay eggs all over your plant and once they hatch your grow will be covered in tiny little 1mm worms that will devour your plants’ leaves, leaving them almost transparent. It’s almost as if they leave the fibers of the leaves and only eat the green parts.

Once they grow bigger, they become easier to detect and many times, growers don’t notice them at all until they grow a bit bigger. They will no longer only eat the green bits; they’ll begin to take entire bites out of the leaves, leaving little cuts similar to those left on apples by the same kind of caterpillars. Apart from eating the leaves, the caterpillars will begin eating the buds as well once they’re a bit bigger, making tunnels and caves through them which allow humidity into the bud and generally, all of the weed where these little buggers have been will rot.

They don’t just rot due to the bites taken out of them; caterpillars defecate all over your plants, and this can only mean bad news. The feces makes it much easier for fungi like botrytis to infect your plant, and it’s generally this kind of fungi that ends up killing off your plants when you have a caterpillar infestation. The feces are quite visible, little 1mm balls all over your plants and buds, stuck to the resin. If you can see the feces then you’ve got some monster caterpillars roaming your grow.

The caterpillars come alive at night and camouflage themselves during the day. When they’re small you can still find them during the day time, and they look like little moving pistils. You can find them under the leaves or even sitting on top of a leaf perfectly camouflaged; you can even find them showing down on your leaves in the middle of the day. Once they’re adults they eat at night time and they go down into the soil during the day so the plant can’t see them; they spin a little silk line that attaches them from the soil to the plant itself, so you won’t see them during the day until they make their cocoon underneath the leaves, but we highly recommend that you don’t let it get that far.

The best way to get rid of them is to avoid them all together by using a preventive product, which is the same product you can use to kill them off if you catch them too late. This product is Bacillus Thuringiensis, a bacterium that burns the stomach of the caterpillars and basically melts them from the inside out, drying them up completely. If you spray at the start of the summer and keep spraying every three weeks, then you should have caterpillar-free plants. If you wait, however, and your plants get infested, you might have to kill most of them by hand as the bigger caterpillars won’t be killed by Bacillus Thuringiensis, they’ll just be slowed down, so you’ll have to hand pick them off which can be kind of disgusting.

If the caterpillars have already made your grow their home, then you’ll need to remove as many as possible by hand, searching through the leaves and buds, as well as anywhere you find feces or bite marks. If you check on your plants first thing in the morning you might just manage to find most of them, as during the day you’ll only find small ones. You’ll need to spray Bacillus Thuringiensis once a week for three weeks in a row to make sure all of the small caterpillars are gone, and then all you have to do is search for the big ones until bite marks stop appearing; if you’re a grower, then you’ll know your plants from top to bottom and you’ll be able to tell when new bite marks appear. During the day it’s much easier to see them if you look at the bottom of the leaves from underneath the plant; the sunlight will highlight any possible caterpillars hiding there. If you wait too long to kill them or you don’t notice them in time, it will be too late and they’ll end up rotting your entire plant, and grow if you’re unlucky.

There’s not much else you can do other than prevent it from happening, as these creatures are natural and go through their life cycle every single year, so if you’re growing outdoors you’re going to need to start worrying about preventing these little hellish worms from appearing on your plants. If you want more information about Bacillus Thuringiensis, click here.

Author: Javier Chinesta
Translation: Ciara Murphy

Getting rid of caterpillar infestations in cannabis grows is easy enough if you catch them in time; if not, you'll need to act quickly.