Cannabis Pests Identification & Control [Expert Guide 2021]

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Cannabis Pests
Author avatar By Parker Curtis
September 22, 2021
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Cannabis pests are common for any gardener, whether you’re growing marijuana or tomatoes. While some insects are beneficial to plants, many can harm them. If you have a pest problem and leave it unaddressed, it can completely kill your ganja. 

Let’s look at why and how you can prevent various marijuana pests.

Why you must get rid of marijuana pests ASAP

Insects like ladybugs, bees, and flies help with pollination and don’t damage your plants in the process. In general, though, most bugs in weed drain your plants of nutrients or remove entire limbs. As you can imagine, cannabis pests aren’t very good for your weed. 

Keeping the bugs on marijuana plants to a minimum is essential if you want good yields. An encroaching snail or stray grasshopper can make short work of your plants. While they won’t destroy your plant immediately, the damage builds up. Eventually, if they’re allowed to do as they please, you’ll be sitting with a marijuana pest infestation.

Cannabis pests control
Cannabis pests control

How to prevent the most common cannabis pests

Each cannabis cultivation method has different ways of stopping and preventing common cannabis pests. You can use many prevention methods in any setup without success being dependant on how you grow your weed. We’ll look at which solutions work best based on specific marijuana pests and the cultivation environment.

Growing indoors

Generally speaking, indoor setups aren’t as prone to weed bug infestations as outdoor gardens. On the other hand, they’re more susceptible to mold and fungal infections. When you’re growing cannabis indoors, you need to keep your humidity balanced. 

Growing outdoors

Unlike indoor areas usually protected from marijuana bugs, outdoor setups leave your plants at the mercy of mother nature. You’re thus more likely to find snails or grasshoppers that nibble away at leaves. On the plus side, mold isn’t as much of a threat in these conditions.

How To Get Rid Of The Dreaded Spider Mites On Plants
Spider mites – Macro View

Cannabis pests chart

Cannabis pests affect your plants differently in the early stages. The damage they cause also sometimes looks different than you might expect. Cultivators often confuse infestations with nutrient deficiencies because they can look so similar. Here’s a cannabis pests chart that gives a brief overview of the most common plant symptoms and their causes.

SymptomCannabis pests identification
Whiteish fuzzy patches under leavesAphids
Scaly, shelled bugs under leaves and branchesBarnacles / Scale Insects
Wilting leaves, brown spots on leavesBroad Mites
Gray, brown, or white powdery flowers with crispy insidesBud Rot, Mold, and White Mold
Bite-shaped holes starting in the center of leavesCaterpillars & Inchworms
Small holes in leavesCrickets
Damaged roots, premature wilting, and surrounded by fungus gnatsFungus Gnats
Chewed or missing leavesGrasshoppers
Whitish “pimples” and white spots on leaves.Leafhoppers
Maze-like, hollowed-out tunnels in leavesLeaf Miners
Yellow, brown, and black spotty patches on leavesLeaf Septoria / Yellow Leaf Spot
Sticky threads and bite marks on leavesMealybugs
White cotton-like coating with many small bugsPlanthoppers
Curled and browning leaves with mites visible under a microscopeRusset Mites
Slimy trails and damaged leavesSlugs / Snails
Small spots, bumps, webs between the leavesSpider Mites
Chewed flowers with silver streaks and specksThrips

The 17 worst weed pests and how to eliminate them

Experienced cannabis cultivators are familiar with bugs in weed while they’re growing. It’s not a train-smash if you find a few mites or a snail in your garden. The trick is dealing with them before they become a problem. Here’s our list of the 17 worst cannabis pests and how to get rid of bugs on weed plants.

1. Aphids

Aphids are tiny, pale little weed bugs that are extremely annoying. They cling underneath the leaves, making them hard to spot. They leech your plants’ nutrients and multiply fast. Left unchecked, they can destroy the foliage in a matter of weeks.

Symptoms

These cannabis pests gather in small patches that look like white specks underneath leaves in the early stages. At first, there may only be a few, but they tend to spread quickly. After a while, you’ll notice your leaves develop brown spots where the aphids were, with the affected leaves eventually dying.

How to treat

If they haven’t spread too much, you can cut away any parts that are infected with marijuana bugs. It’s not recommended, though, as you can hamper your plants’ growth. An alternative is to remove aphids by using lukewarm soapy water and a soft cloth. As tedious as it sounds, you might need to wash them off all the leaves.

You can prevent future outbreaks by introducing ladybugs into your ecosystem. They love eating aphids and have no negative impact on your weed.

2. Barnacles / Scale Insects

Scale insects are strange weed bugs that chill under leaves. They bite into your plant and suck all the food straight out. In due time, your marijuana doesn’t get enough nutrients and wilts.

Symptoms

If you see small, shelled cannabis insects under the leaves, you probably have barnacles. They don’t cluster too much and can take time to reproduce. Leaves slowly lose color as nutrients are drained, and they die afterward.

How to treat

You must remove scale insects before they spread and cause a problem. Unfortunately, you’ll have to manually check your plants thoroughly to ensure you don’t leave any behind. As far as marijuana pests go, they’re manageable, but colonies shouldn’t be allowed to develop.

3. Broad Mites

Broad mites are microscopic bugs that feed off young plants. Like other cannabis pests, they aren’t there to help your weed grow. You need to take notice early and stop them before they decimate your crop.

Symptoms

New growth might become bent and twisted, blistered, or wet-looking. Edges of leaves turn upwards and turn yellow. During the budding phase, colas look sick and die before flowering completely.

How to treat

You can use miticides to treat and prevent these insatiable weed bugs. Avoid spraying the flowers because you probably don’t want to smoke pesticides. Owners of setups can adjust temperatures to 90°F (32°C) for an hour or so. Broad mites die very easily from overheating at these temperatures.

Alternatively, you could introduce Neoseiulus, which are predatory insects that feast on broad mites. However, they’re more suited to prevention than the removal of cannabis pests.

4. Bud Rot, Mold, and White Mold

Bud rot, mold, and white mold tend to only appear in specific areas. Less of a marijuana pest than an infection, flowers are most often affected. The most common causes of moldy plants are high humidity, combined with poor ventilation.

Symptoms

If your weed has bud rot, the flowers will start darkening and crumbling. Mold and white mold are weed pests that create a powdery layer on various parts of the plant. If you break the buds, the inside will be browned, crispy, and filled with powdery spores.

How to treat

Trim away any parts already infected with mold and bud rot. The key to preventing mold in indoor setups lies in maintaining low humidity and having good ventilation. Outdoor growers can buy climate-specific strains and cover their plants when it rains to prevent moisture in buds.

Bud rot with a dead caterpillar
Bud rot with a dead caterpillar

5. Caterpillars & Inchworms

Caterpillars and inchworms are common cannabis pests. Although some may look cute, they’re not very considerate. Given the opportunity, a caterpillar will eat your entire ganja plant without a second thought.

Symptoms

Caterpillars start eating leaves from the middle outwards. You’ll notice holes in the foliage where the caterpillar was. If you don’t stop these weed bugs, all the leaves will be gone in a few days.

How to treat

You can use caterpillar “BT” spray to kill and stop caterpillars. It focuses on worms, moths, and larva without harming other insects. Alternatively, spinosad is organic and 100% safe. You can spray it on leaves, directly on the caterpillars, or on the soil.

Keep learning about how to get rid of caterpillars with this awesome video by yours truly:

6. Crickets

You might not realize how annoying crickets are, but they’re a frustrating cannabis pest to control. The chirping has a cute appeal, but not in your house. Not only that, they’ll eat your plants bare.

Symptoms

At first, you might not even notice any visible damage that these weed bugs cause. They create small holes that are easily overlooked. If they’re left alone, they’ll multiply and cover the foliage in holes, killing your plant.

How to treat

Cricket bait and traps are quite effective at catching these marijuana pests. They won’t stop an infestation but should reduce numbers and can keep crickets away from your plants. Other alternatives like neem oil and pesticides are also options you can consider. However, if you’re consuming a product, pesticides aren’t always the best way to go.

Crickets are one of the most dangerous pests to cannabis plants
Crickets are one of the most dangerous pests to cannabis plants

7. Fungus Gnats

Fungus gnats look a bit like fruit flies. As a weed pest that mostly affects indoor crops, you’re likely to notice their presence before the damage they cause. They lay their eggs in moist potting soil, which can be hard to spot before they hatch.

Symptoms

In small numbers, they’re not so bad. If their population grows too large, they become cannabis pests that devour plant roots. Seedlings are the gnats’ favorite targets and therefore die before they can mature.

How to treat

You can use apple cider vinegar or sugar water traps to lure adult fungus gnats away from your plants. Their lifespan is only about a month, but they can lay thousands of eggs in that time. While they’re not the worst marijuana pest globally, the threat lies in their rapid population growth.

How to Get Rid of Fungus Gnats
Fungus Gnats

8. Grasshoppers and Locusts

They’re some of the most vicious cannabis pests out there. They can cause infestations of biblical portions and run through a crop in a matter of hours. If you notice damaged leaves, you have to take immediate action.

Symptoms

Grasshoppers and locusts are weed pests that cause damage similar to snails but in bigger proportions. The main difference is that they don’t leave a slimy streak behind. Instead, they might leave nothing behind at all. If you see severely eaten leaves without snail trails, you might be facing grasshoppers.

How to treat

As with many other weed insects, neem oil or Pyrethrin based insecticides are good at killing off crickets and locusts. Insecticidal soap also works but is a less popular choice. The best you can do to keep locusts and grasshoppers at bay is to create a thin gauze covering your plant to stop any pests. If you’re brave enough, you can also catch them and kill them on the spot.

9. Leafhoppers

These cannabis pests are hard to spot, and they’re essentially everywhere. They drink the sap from your plants, removing much-needed nutrients. Fortunately, you can stop them from damaging your plants.

Symptoms

When they lay eggs in the stems and leaves, you’ll notice bumps that look like pimples. Adult leafhoppers inject toxic saliva into the plants when they feed, leaving white spots. After a while, damaged leaves die prematurely.

How to treat

Organic neem oil is a fantastic solution in stopping these marijuana pests. Keep applying neem oil throughout the early stages to prevent future infestations.

10. Leaf Miners

Leaf miners are a horrible marijuana pest. If you spot signs of leaf miners, you need to address the problem immediately. Beyond that, they disfigure your plants and can kill them in a matter of weeks.

Symptoms

Yellow or brown maze-like trails on leaves are a clear indication of leaf miners. They also tunnel their way through your leaves until there’s nothing left. These weed bugs live in the foliage and eat the insides, hollowing them out.

How to treat

Cut off any affected foliage, and remove the plants with leaf miners from the rest of the crop. You can use neem oil or regular pesticides to kill any remaining miners.

Prevention is always better than a cure when it comes to any cannabis pest. Sticky traps are a great way to lure adult leafminers before they can lay eggs. Alternatively, floating row covers for outside crops keep pests off your cannabis plants

11. Leaf Septoria / Yellow Leaf Spot

Yellow leaf spot is a truly terrifying marijuana pest. Like mildew and white mold, it’s a fungus that slowly creeps over your plant. If you’re observant and fast to react, you can stop pests and bugs before your plants die.

Symptoms

Early on, yellow and brown spots will form on both sides of the leaves. The spots have dark outsides with lighter middles. Plants entering their flowering phase are usually the victims of this weed pest.

How to treat

Like other fungi, high humidity and bad ventilation are the usual culprits. By keeping the environment dry and the air flowing, you can prevent a fungal infection. Unfortunately, you’ll have to remove all infected foliage because it can spread to other areas.

12. Mealybugs

Mealybugs are squishy, wingless insects. They’re often pinkish-purple but become white after covering themselves in a cottony wax layer. You might think they look cute at first until you realize the damage these cannabis pests can cause.

Symptoms

When they start infecting plants, you’ll notice some puffy blobs on your plant. After a while, they start creating sticky threads on the leaves as they move around and eat. Left long enough without treatment, they consume the weed leaf entirely and migrate to other areas of the plant.

How to treat

A good way of getting rid of these cannabis pests is alcohol. An alcohol-soaked cotton swab kills them instantly. You need to go over every inch of your plant and keep it isolated to prevent a spread.

13. Planthoppers

Baby planthoppers look a bit like hermit crabs and adults like small moths. These bugs live on weed plants and turn them into what resembles a spider’s nest mixed with a butterfly cocoon. Truly the stuff of nightmares, you should get rid of them as soon as you spot them.

Symptoms

Leaves and buds become covered in a sticky webbing, and the little cannabis pests crawl around. When they eat, they bite into leaves and branches, sucking the nutrients out. Foliage dies, and eventually, your weed plant looks like Frodo carried it through Shelob’s lair.

How to treat

Fortunately, you can use conventional pesticides to get rid of these weed bugs. Smokable weed shouldn’t be sprayed, and if possible, use organic options. You could also use traps to lure the adults, thereby controlling their population.

14. Russet Mites

Russet mites are cannabis pests that usually come from outside your crops’ immediate surroundings. They hitchhike on other insects, float with a breeze, or hang out on your clothes. When it comes to the identification of cannabis pests, they’re often easily overlooked.

Symptoms

Symptoms look similar to nutrient deficiencies or overwatering. Leaves often look burnt, yellowed, or curled up. You’ll need a handheld microscope to see these little critters. They’ll be lined up next to the veins of the leaf.

How to treat

Isopropyl and Rubbing Alcohol are very useful in killing adult russet mites. General pesticides also kill them, with organic ones being preferred by most cultivators. You’ll also need to remove foliage infected by these weed pests to stop them from spreading.

Russet Mites
Russet Mites on Weed Leaves

15. Slugs / Snails

Slugs and snails are very common cannabis pests. Regardless of what you grow, there’s a good chance you’ll encounter them. They’re ruthless in their consumption and are very sneaky.

Symptoms

Snails and slugs leave a glistening trail everywhere they go. They munch leaves from the outside inwards and wreak havoc if ignored. If you notice signs of snails, you need to act immediately.

How to treat

You can put salt in a large ring around your plant pots to prevent snails or slugs from going to them. Salt is deadly to them and will make these weed pests steer clear of your plants. An odd solution that appears to work is beer.  Slugs and snails are attracted to beer for some reason.

You can make a trap using an empty can and lure them away from your plants. When they climb up the tin to reach the beer inside, they fall in and drown in beer. Keep the tin above ground level to prevent friendly insects from accidentally joining the snails.

16. Spider Mites

Spider mites are tiny and look a little endearing. You can easily identify these cannabis pests by their unique appearance. They look like see-through minuscule spiders and leave silk webs everywhere.

Symptoms

The first things you can see are the small eggs underneath the leaves of your weed. They also cause yellow spotting where the mites feed, which is often confused with other marijuana pests. The longer you leave them, the more they’ll multiply, eventually enveloping your plant in webs and eggs as it dies.

How to treat

Depending on how far they’ve spread, solutions range from using pesticides to simply burning the whole plant. The best option is prevention, which you can do by having airflow that keeps them away. Stagnant, humid air is the perfect breeding ground for cannabis pests.

Hatched Spider Mites
Spider Mites on a leaf

17. Thrips

Thrips look a bit like ants with long abdomens and a pair of wings. They have asymmetrical mouthparts; one mandible is longer than the other. These marijuana bugs use their mouths to pierce the plant and extract the sap. Streaks, silver speckles, and small white patches are indicators that thrips were in your weed.

Symptoms

Chewed colas are the first signs of a thrip infestation. The damage they cause to buds reduces yields and hinder plant growth. They also carry plant diseases that can be fatal to your weed.

How to treat

You can use sticky traps, pesticides, or dormant oil on your plants to get rid of thrips. Alternatively, shake your plants and catch any weed bug that drops. To kill them, you can throw them in a bucket of hot water. If none of the above sounds good to you, use diatomaceous earth to dust the undersides of leaves.

Thrips Pest
Thrips Pest – Macro View

Key takeaways about cannabis pest control

Taking care of your marijuana is the first step in cannabis pest control. Maintaining the humidity and temperature levels is the best way to prevent various infections. Ensuring your buds don’t get wet also keeps them from going moldy. 

Daily checkups can dramatically help prevent infestations. Looking under your leaves every day and noting the color of the foliage are easy ways to spot the effects of weed pests. 

Sites like the Homegrown Cannabis Co. allow newbies to learn more about becoming better cultivators and ultimately helping them to prevent diseases and pests. Also visit our Homegrown Forum to learn from other growers’ mistakes. 


About the author: Parker Curtis

Parker Curtis has around a decade of cannabis-growing experience, specialising in soil-less and hydro grows. He’s mastering outdoor, greenhouse, and indoor grows.