Pests, Bugs & Viruses

Last updated Jan 30, 2024

by Nebula Haze

Unfortunately, common cannabis bugs and other garden pests can totally mess up your marijuana harvest.

Caterpillars are one of the most common cannabis pests when growing weed outdoors. Use BT Caterpillar spray (works best if you apply with a mister) as a safe and effective way to eradicate them for good.

This page aims to be a comprehensive resource on the different types of bugs / pests / mold that can affect your marijuana crop, along with tips for preventing and solving each problem.

Pests that can affect your marijuana plants include aphids, fungus gnats, thrips, green flies, black flies, mosaic virus, spider mites, caterpillars, inchworms, whiteflies, white powdery mildew / white powdery mold, stem rot, and even mammals such as deer or cats!

If you want a list of safe, all-natural pesticides that can get rid of most of the pests on this list, check out this page: https://www.growweedeasy.com/safe-cannabis-pesticides

It’s time to fight back against cannabis bugs, mold and pests!

Quick Tip! Whenever you spray plants with anything, make sure to get the undersides of the leaves too, as this is where many pests like to hang out! A sprayer / mister is also really helpful for spraying leaves.

Get a mister to evenly spray cannabis plants with an insecticide.

Buy a water mister to spray cannabis plants with bugs

 


 

Aphids

Aphids live under leaves and have different forms depending on their stage of life. They are skinny and white when young and fat and plump as adults. Often green, but sometimes other colors like red or black.

Examples of aphids in different forms of life, including larvae, nymphs and adult aphids - They have colonized the back of this cannabis leaf!

Example of an adult aphid and nymphs. You can see the outline of the adult aphid on the right side of the picture.

Example of a winged aphid resting on a leaf - get rid of these "colonizer" aphids before they lay eggs on your cannabis plants!

 

Barnacles / Scale Insects

These bugs that look like barnacles and stick to the plant on stems and underneath leaves

Example of barnacles / scales on a cannabis plant

 

Broad Mites

These mites are so small you will likely never see them even under a magnifier. However, you can tell your plant has been infected because your new leaves will be blistered, twisted and glossy. The overall plant will also be growing poorly and if it’s flowering the buds may turn brown. Broad mites are often mistaken for other problems like nutrient deficiencies, heat stress or pH problems.

Example of leaf damage from broad mites or russet mites

 

Bud Rot or Mold

When bud rot strikes, certain buds may start looking sickly overnight, with leaves turning yellow and/or bud becoming discolored. When opened up the inside of the bud is dead or moldy.

Example of a marijuana cola with a bad case of bud rot - the inside of the bud has turned brown, and the outside leaves are dying

Example of a cannabis bud / cola with mold - this is what causes bud rot

Example of a small outdoor cannabis cola that has been infected with bud rot. You can see the wetness of the leaves around the bud - wetness is a major trigger for mold and bud rot

 

Caterpillars, Inchworms & Cabbage Loopers

Caterpillars and worms eat holes in leaves, which is typically the main symptom most growers see.

Example of leaf damage inflicted by a caterpillar / inch worm on a marijuana leaf

Example of an inch worm / caterpillar on a cannabis leaf. You can even see a hole in the leaf where it was eating! Grrrrrr

Caterpillars leave droppings that look like black specks. If you see this, you know you’ve got caterpillars.

Examples of caterpillar poop - they leave these black speck on your leaves, which can be easily wiped off

 

Crickets

“Regular” crickets will munch on your leaves while “mole crickets” can tunnel under your plants and disturb their roots!

“Regular” Crickets

Example of a cricket in its larva form on a cannabis leaf

Example of a green cricket - an annoying cannabis pest!

Mole Cricket – these can tunnel under your cannabis plants like moles

Example of a mole cricket, which is a marijuana pest that can tunnel under your plants and disturb the roots!

 

Fourlined Plant Bugs

This is the cannabis leaf damage from a four-lined plant bug (Poecilocapsus lineatus). You can see the adult version of the bug on the lower left. Both the adults and their nymphs make spots in cannabis leaves that usually appear in clusters.

This is the cannabis leaf damage from a four-lined plant bug (Poecilocapsus lineatus). Commonly misdiagnosed as leafhopper or planthopper damage. You can see the adult version of the fourlined plant bug on the lower left. Both the adults and their nymphs make spots in cannabis leaves that usually appear in clusters.

 

Fungus Gnats

Fungus gnats look like tiny dark flies. They hang around soil that stays wet for long periods of time, and their worm-like larvae crawl around in the wet top soil. Plants start getting sick if a gnat infestation gets out of control.

Example of a tiny fungus gnat - luckily these cannabis pests are not too serious and are easy to get rid of

Example of damaged and yellowing leaves caused by a big fungus gnat infestation

 

Grasshoppers

You’ve probably seen these before, but these seemingly harmless garden creatures will happily eat your cannabis leaves!

Example of a grasshopper on a cannabis leaf - these pests eat holes in your leaves!

 

Leafhoppers

These bugs come in almost every color and form, but they all cause “leafhopper burn” on your plants if their numbers get out of control.

Leafhopper cannabis damage (“hopper burn”)

 

Leaf Miners

Leaf miners are larva that actually live inside your leaves and tunnel through them to eat!

Example of leaf miner damage on a cannabis leaf - these pests leave little lines or trails where they have tunneled through your leaf

 

Leaf Septoria / Yellow Leaf Spot

This fungus causes round yellow or brown spots, with symptoms often starting on lower parts of the plant

Leaf septora causes small yellow, brown or dark spots on the leaves - and is the result of a fungus infection

 

Mealybugs

These tiny white bugs look “hairy” and are found crawling on leaves and buds.

Example of a hairy white mealy bug on a leaf - this cannabis pest can get out of hand quick!

Hairy white mealy bug crawling on a cannabis leaf

 

Planthoppers

Each species looks quite a bit different as an adult. Some look like pretty leaves. As youngsters, they create white and fuzzy patches that look like cotton on their butts and on your plants. Planthoppers suck the life out of cannabis plants if they start a colony.

Planthopper nymphs produce a white substance that is reminiscent of cotton or even mold

Planthoppers are common cannabis pests - main symptom is white fuzzy patches, bugs take many forms

Example of a planthopper larva with white waxy secretions

The following are two examples of adult planthoppers (can take many adult forms, though symptoms are the same)

Example of a green planthopper with a white larva

 

Root Rot

Root rot is a common problem in hydroponic systems though overwatered plants in containers often display similar symptoms. Plants with root rot wilt and leaves may become discolored. In the reservoir the roots turn brown, smelly and slimy.

Example of hydroponic cannabis plants wilting due to root rot

Cannabis roots with root rot (slime) :(

 

Russet Mites (or Hemp Russet Mites)

Russet mites are so small you can only see them with a magnifier unless there are thousands of them infesting your plant. They live in the crevices of leaves, stems, or buds.

Hemp russet mites on cannabis symptoms (yellow mass of bugs, tops of plants droop)

Hemp russet mites on cannabis can cause the edges of leaves to curl in, and buds to die

Cannabis plant with hemp russet mites

 

Slugs / Snails

Slugs and snails usually come out at night, leaving holes in leaves with scalloped edges from their individual bite marks. They also leave slime trails on leaves and on the ground.

Example of a snail on a leaf. Notice it has left a trail of slime, and also that all the holes in the leaves have scalloped edges

Slug damage on cannabis leaves

 

Spider Mites

Spider mites are often caught from another cannabis grow room, and their bites leave small white speckles all over your leaves. The bugs are so small they can be hard to see, though the best place to look is underneath leaves.

Spider mites leave small yellow or white specks on cannabis leaves that are round looking

Example of spider mites and their eggs on the back of a cannabis leaf

You may see webbing when enough spider mites are living on the cannabis plant.

Example of webbing on a cannabis bud caused by spider mites

 

Stink Bugs

Various species of stink bug have been known to attack cannabis plants. They lay distinctive patches of white eggs, which hatch into small beetle-like insects and eventually grow into stink bugs.

Young stink bugs massing on eggs that were laid on cannabis leaves

Eggs on cannabis leaves caused by the conchuela stink bug (Chlorochroa ligata)

 

Thrips

Thrips leave irregular bronze or silver marks that may look like “dried spit” or tiny snail trails. It is also commonly mistaken for a cannabis nutrient deficiency, environmental stress, or other problem.

A cannabis leaf with thrips damage

Young thrips are tiny and look like fat, squirmy worms living on your cannabis leaves.

A young (nymph) thrip looks a lot like a tiny, fat worm

 

Tobacco Mosaic Virus

It’s not known whether mosaic virus has jumped from tobacco to cannabis plants, but in this article, I’ll share what I’ve learned so far…

Example of cannabis leaf symptoms that may or may not be caused by TMV (tobacco mosaic virus)

 

Whiteflies/ White fly

Whiteflies look like tiny white moths and hang out under your cannabis leaves.

Marijuana white fly infestation on a cannabis leaf

Example of a white fly - get rid of this common cannabis pest!

 

White Powdery Mold

WPM leaves a white powdery substance that looks like flour or powder on leaves and stems

Example of white powdery mildew (WPM) on a cannabis leaf

 


 

Don’t see your bug here? Send us a pic!

 


 

Jump to…

Diagnose Your Sick Plant!

7 Steps to Cure 99% of Marijuana Growing Problems

Beginner’s Guide to Growing Weed

How to Improve Your Yields

 


 

 

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