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Common Pests on a Cannabis Plant

Updated September 6, 2022

Contents


  • Aphids
  • Barnacles and Scale Insects
  • Broad or Russet Mites
  • Spider Mites
  • Caterpillars and Inchworms
  • Crickets
  • Fungus Gnats
  • Grasshoppers
  • Leafhoppers
  • Leaf Miners
  • Mealybugs
  • Slugs and Snails
  • Thrips
  • Whiteflies
  • Removing Pests with a Power Sprayer
  • Using Insecticide
  • Be Wary of Chemicals
  • Avoid the Buds
  • Pyrethrin Is Popular
  • Using Spinosad
  • Using Neem Oil
  • Using Alcohol
  • Using Diatomaceous Earth
  • Controlling Pests with Traps
  • Applying Pest Control
  • Applying Floating Row Covers
  • Consider Beneficial Insects
  • Removing Damaged Plants or Infested Parts
  • Conclusion

When growing cannabis, you need to learn everything you can to keep your plants healthy. In addition to proper nutrition, watering, and light, you should also be aware of the pests that can harm your plants.

Learn more about the common pests that you may find on cannabis plants and the damage they might cause. From there, you can learn how to avoid problems due to pests, so your cannabis plants grow healthy and potent.

Aphids

Aphids might live underneath the leaves of your cannabis plant. These may be brown, red, black, yellow, green, or white and can affect cannabis plants all around the world. Aphids produce a sweet liquid called honeydew, which can attract sooty mold.

Barnacles and Scale Insects

Barnacles will stick to the stems of your cannabis plant as well as under the leaves. Barnacle scales do not move much, but they will suck the life from the leaves and stems of your cannabis plant. These pests also release a sticky-sweet honeydew that can attract ants. That honeydew may also lead to sooty mold forming on the plant in dark patches.

Broad or Russet Mites

The mites are incredibly small to the point that you are unlikely to notice that they are on your cannabis plant unless you grab a magnifying glass. Even then, you may not spot them. Most growers only notice mite infestations when the new leaves become twisted, blistered, and glossy. Plants infected by mites will also grow poorly. In the case of flowering plants infected with mites, the buds might turn broad. You may even notice that the leaves look wet or are turned up at the edges.

Because of the overlap in symptoms, it is common to mistake mites for issues like pH imbalances, nutrient deficiencies, and heat stress. Broad mites will concentrate their attack in specific areas so the damage is not evenly distributed throughout your cannabis plant.

Spider Mites

Close up view of a spider mite.
Close up view of a spider mite.

Another type of mite commonly found in cannabis plants, spider mites frequently spread between grow rooms. You can recognize their presence since their bites will leave behind small speckles on the leaves. Spider mites are small enough to be very hard to see, although you are more likely to spot them underneath the leaves. If there are enough spider mites on a cannabis plant, you may also notice webbing.

Spider mites are one of the least-liked pests on cannabis for many reasons. It is common to think you got rid of them, only for them to reappear later. They also eat a lot and reproduce quickly. They will also quickly become immune to your chosen treatment method. As such, you need to eliminate all of them on your first try.

Caterpillars and Inchworms

Worms and caterpillars can damage your cannabis plant by eating holes in the leaves. You may notice their presence because they leave droppings that appear as small black specks.

Crickets

Crickets can eat your cannabis leaves, damaging the plant. There are also mole crickets that tunnel underneath plants, harming their roots. The good news is that crickets are less likely than most of the other pests on this list to harm your cannabis plants.

Fungus Gnats

A fungus gnat in its larval state.
A fungus gnat in its larval state.

Fungus gnats look similar to tiny flies that happen to be dark. They tend to appear in soil that remains wet for a long time. Their larvae are worm-like and will crawl in the damp soil on top. If you let a gnat infestation get too far, then your plants will start to get sick. Fungus gnats are one of the easier pests to remove from the plants. Because they are attracted to over-watered soil, you can typically discourage them by merely reducing your watering, so the plants do not get too much.

Grasshoppers

You may not realize it, but grasshoppers may start eating your cannabis leaves. Grasshoppers can cause significant damage when they appear in larger numbers.

Leafhoppers

Leafhoppers can appear in most colors, making them sometimes hard to recognize. You can tell that your cannabis plants have leafhoppers if you notice oddly-colored clusters on the leaves. These are the locations where the leafhoppers sucked the sap out of your leaves.

Leaf Miners

Leaf miners are a type of larva that lives inside the leaves of your cannabis plant. They eat by tunneling through the leaves, leaving grayish twisting lines of discoloration. Interestingly, the term leaf miners refer to multiple types of larva that produce similar results by eating the leaves on the inside. The bugs then grow up to become other pests on this list.

Mealybugs

Mealybugs are small white bugs that appear hairy. You may spot them on your cannabis buds or leaves. Mealybugs are yet another pest that will produce honeydew, a sweet liquid. This honeydew may encourage the growth of mold, giving you even more problems with your cannabis plants.

Slugs and Snails

It is more likely for snails and slugs to attack your cannabis plants at night. They will bite through the leaves, leaving behind holes. You can recognize holes from slugs or snails based on the scalloped edges that result from the pests’ bite marks. You may also spot slime trails on your plants’ leaves and the ground by the plants. A single slug or snail will not do too much damage to your plant, but larger numbers can cause significant damage.

To make matters worse, slugs and snails will not just eat the leaves on your plants. They may also eat the buds, which are likely the reason that you are growing cannabis.

Thrips

Thrips are small pests that leave behind silver or bronze marks that are irregular. These marks may appear as tiny snail trails or dried spit. Young thrips look similar to small, fat worms.

Whiteflies

Whiteflies appear similar to small white moths. They tend to be found underneath your cannabis leaves instead of on top of them.

Removing Pests with a Power Sprayer

In many cases, you can start getting rid of the pests on your cannabis plants with a power sprayer. These will physically force the bugs off of the plant.

Using Insecticide

You can also use insecticides to kill the pests on your plants. Various insecticidal soaps tend to work best on different types of insects, so read the label.

Be Wary of Chemicals

Just be careful when choosing the insecticide to use. You don't want to select a product with harsh chemicals as some of these may end up in your cannabis.

Avoid the Buds

To minimize the risk of contaminating your cannabis when using insecticides, you should do your best to avoid spraying the products on the buds. This reduces the risk of some getting into the part of the plant you plan on smoking, but there might be residuals.

As you look at the various insecticides available, you will notice that pyrethrin-based insecticides are common. They degrade quickly and are minimally toxic to humans. They are a standard control method in vegetable gardens. The issue with pyrethrins is that they are also toxic to bees, which we want to preserve. To overcome that to some extent, make sure to use these products only if the sun has already set, as the bees should be asleep, and the pyrethrin will break down before the bees wake up.

Using Spinosad

An alternative to chemical insecticides is Spinosad products. These can work against aphids, spider mites, whiteflies, caterpillars, and thrips. The products are entirely organic and will not harm the plants or your children or pets that may be nearby.

Proponents of Spinosad point out that using it comes with almost no adverse effects thanks to its organic nature. The only thing to remember is that you will need to mix the products the day you use them since they tend to only be useful for about 24 hours following mixing.

Using Neem Oil

Some people also suggest using neem oil as a natural treatment for a range of pests that can affect cannabis plants. The good news is that neem oil is all-natural and works on a variety of bugs in addition to problems like mold.

The thing to remember, however, is that you do not want to let neem oil anywhere by the buds as it will leave an unpleasant smell and taste. As such, you should use it with care. You should also keep in mind that neem oil can be hard on plants, so you should use it as much as necessary, not more.

Using Alcohol

For some types of pests, you can use alcohol to control them. This is the case for mealybugs, as alcohol will dry out the bugs’ protective outer coating, which is waxy. You can apply the rubbing alcohol to a cotton swab and use that to kill each bug. You can also use an alcohol spray on the plant.

Using Diatomaceous Earth

Depending on the pest threatening your cannabis plant, you may also want to consider using diatomaceous earth. This is fossil dust that you put on your soil. You can also spread it anywhere else that you do not want the pests to cross. It is harmless for plants and mammals, but it causes severe dehydration and harm to many pests, like broad mites. It is good at controlling and preventing pests but not removing an existing infestation.

Controlling Pests with Traps

There are also some traps that you can use to control certain types of pests that may affect your cannabis plants. For example, you could make a trap for slugs with a saucer of beer. The slugs will be attracted to the beer and then drown in it. You can also purchase traps for specific types of pests, although there will not be options available for all types.

Applying Pest Control

Most cannabis growers will apply pest control solutions to prevent and eliminate pests from their plants. When you use them, ensure that you spray your solution on the bottom of the leaves in addition to the top part. It is common to forget about the underside of the leaves, but this is a serious mistake. After all, many pests prefer to spend time under the leaves instead of on top of them. As such, make sure that you spray the entire plant to control the pests effectively.

Applying Floating Row Covers

Another solution to control pests on your cannabis plants is to opt for floating row covers. These are not ideal for all growers, but they can be an affordable and effective solution. Floating row covers will physically prevent most types of pests, especially the larger ones, from getting to your plants.

At the same time, floating row covers are thin enough to let light to your plants. You can even water your plants through them. You will notice that floating row covers are much easier to use with smaller plants than bigger ones.

Consider Beneficial Insects

Ladybug eating a spider mite.
Ladybug eating a spider mite.

You should also consider using beneficial insects to deter the common pests on your cannabis plants. For example, ladybugs and lacewings can eat scales, which would otherwise cause damage to your plant.

Removing Damaged Plants or Infested Parts

In some cases, you will have to get rid of the plants or portions of your cannabis plants that have been infested by pests. This is the case, for example, with broad mites as they create too much damage for the plant to overcome in that area. In the case of broad mites, you are unlikely to save the damaged parts of the plant, so you want to stop the pests from spreading. You will also want to remove the affected leaves if you are dealing with leaf miners.

Conclusion

Many types of pests can affect your cannabis plants. To ensure your plants thrive, you need to take preventative actions to control the pests. You also need to watch out for them, so you can control an infestation while it is still in the early stages. There are numerous control methods available, but use caution with chemicals due to the potential for some residue to remain on the plant.