Pests, Bugs & Viruses

Updated Aug 15, 2021

by Nebula Haze

Unfortunately, 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:

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



Aphids live under leaves & have different forms depending on their stage of life

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 and leave droppings that look like black specks

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

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


“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!


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


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!


These bugs come in almost every color known to man so sometimes it can be tough to tell what they are just from looking. However, they all make clusters of spots on your leaves where they’ve sucked out all the sap, so if you see spots like this you know you’ve got leafhoppers!

Example of leafhopper leaf damage on a cannabis plant. Leafhoppers leave specks all over the leaves where they suck out the sap. This picture is by OvergrowDaWorld


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


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

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 green planthopper with a white larva

Example of a planthopper larva with white waxy secretions


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 the 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 grow room, and their bites leave small white speckles all over your leaves. They’re so small they can be hard to see, though the best place to look is underneath leaves. You may see webbing if there are enough of them living on the plant.

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

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 leave irregular bronze or silver marks that may look like “dried spit” or tiny snail trails. Their young look like fat, tiny worms.

Example of thrip damage on a cannabis leaf

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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