Complete guide to common cannabis pests and how to treat them

Published Jan 25, 2019 05:27 p.m. ET

What are all these bugs on my pot plants? Weed bugs come in all different shapes, sizes, and colors. If you are struggling to diagnose a weed bug than you have come to the right place. Here we will cover some of the most common cannabis pests and exactly how to treat them.

Aphids/ Greenflies/ Blackflies - An aphid, greenfly or blackfly is a soft-shelled bug that can be either white, green, black, brown, yellow, or red but most commonly is describedas little black bugs on a weed plant. These are some of the most widespread cannabis pests in the world since different kinds can be found in almost every region. They are tiny, oval-shaped and practically always have wings. These guys will hang out underneath of your cannabis plant’s leaves where they will attach and feed on the plant. The most common cause of one of these infestations is an adult bug laying eggs which can often go unseen and unnoticed.

The best treatment, in this case, is prevention. While that may not sound great to those who are already struggling with what to do with these little black bugs on a weed plant; routine inspections can help make actual treatment more effective. Prevent these insects from moving in by keeping your plants moist by misting several times a day. If you already have them your best bet will be to wash the entire plant using a gentle room temperature water and gently removing the webs and bunches of insects by hand. The next option is insecticidal soap that contains high levels of fatty acid salt to kill them. This keeps it safe for the plant but weakens the bugs hold on the plant. Neem Oil is also an option but will leave a strong unpleasant smell after use. If using oil be sure to not put any directly onto your buds because it will leave a residue and you do not want to smoke that as it contains ingredients also harmful to humans. The final option is bringing in predator insects that can benefit the marijuana plant while consuming the harmful ones. You can use either other species of aphids with the drawback of a fast reproduction rate, or ladybugs which are both predators of these insects.

Barnacles - If you are wondering to yourself “What are these little white bugs on my weed plants?” Then chances are you are more than likely dealing with Barnacles. These insects can be found under leaves and along the stalks of a marijuana plant. They slowly draw out the nutrients of the plant which can weaken and even kill it if not dealt with. Some barnacles are equipped with a camouflage feature making them appear as growth while others look more like a beetle with a similar shape to that of a potato bug.

Treatment for barnacles is essentially the same as you would treat aphids, by washing off with a power washer. Unfortunately, the majority of barnacles will not be eaten by beneficial predator species. Remove as many of the bugs as you can be using a handheld pressure washer filled with room temperature water, or by running under the tap in a kitchen sink. Fatty acid insecticides are also efficient at wiping out well-established populations as is Neem Oil, but remember oil is unsafe for human or pet consumption.

Broad and Russet Mites - Mites are nearly impossible to spot with the naked eye due to their size. Generally, when an infestation has occurred, it isn’t apparent until the plant has already begun to weaken. Mite infestations present themselves with symptoms such as droopy, yellowed, or hole filled leaves.

Mites can be one of the most difficult pests to treat and will require due diligence in a steady flow of treatments to eradicate them fully. Insecticides rarely work for mites, but what is effective is Neem Oil. Regular three times a day treatments of Neem oil will be required for one to two weeks depending on how many you have.

Fungus Gnats: Fungus gnats look like tiny odd shaped fruit flies that can often be observed hovering over top of growing marijuana plants. Fungus Gnats are cannabis soil pests. Their eggs are hatched in moist soil and can be an issue if the dirt in your plants is never thoroughly allowed to dry.

While it may sound odd, using a hair dryer to dry out the soil in pots is a great first step. This will make it so they will no longer be able to reproduce. A fungus Gnats lifespan is incredibly short. After a few days, you should see a dramatic decrease in numbers. If that isn’t enough than the other option is first based treatments like Neem Oil or diatomaceous earth which will kill the adult bugs on contact.

Leaf Miners - This weed bug lives inside of the plant material of a plant and is not a bug so much as it is the larva of several potential species that lay eggs inside of the leaves of a cannabis plant. The cannabis pests themselves are not visible by regular observation. Instead look for white or yellow lines appearing on the leaves. They will appear messy, and jagged, and a very different color than the leaves themselves.

Begin by removing all affected leaves. Since they are contained within the leaves, this will get rid of most of them almost immediately. Your next step should be an organic insecticide like Spinosad that will kill Leaf Miners when ingested and through contact.

Mealybugs - Mealy bugs are kind of creepy looking. They appear bright white and hairy to the naked eye. These cannabis pests can be found long after the growing stage and can even be spread while a plant is drying.

Begin by removing as many as possible by hand and with water pressure. They won’t bite so you don’t have to worry about touching them. Follow washing with a treatment of alcohol. Use 9 parts water and one-part alcohol mixing in a misting bottle and spray all plants down three times daily until they are eradicated.

Spider Mites - This weed bug is a member of the spider family and is one of the most common among indoor cannabis pests. They are tiny and are generally noticed by either the bite marks left in plants or the numerous piles of webs they use to reach and eat the leaves of a marijuana plant.

Some growers have had success using multiple insecticides, or pesticide oils to kill them. However, the biggest problem with spider mites is they will adapt to withstand anything you use to try and kill them. To rid yourself of a spider mite infestation will likely require 3-6 days of plant washes where as much of the web is removed as possible. This does not instantly kill them, but without webbing, they will have no access to the leaves, so they will slowly die of starvation.

Thrips - These cannabis pests look more like a long tiny grasshopper and can appear black, brown, or yellow. The damage this weed bug will do is long term. The insects will ingest any accessible nutrients from any part of the plants they can, with leaves being the most heavily targeted.

While you may have some success with insecticides due to this bug’s size and fast harmful nature it is best to use a Pyrethrins treatment which is not only the most effective but is also safe for humans and animals. This treatment should take two or three days before you see the thrips disappear entirely.


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