Unfortunately, we are not the only species that enjoys cannabis. When we give them a chance, there are numerous different organisms that can and will comfortably find their home in your garden. From spider mites and mold, to slugs and snails, these invaders can destroy your hard work in no time if left unattended.
Although cannabis plants can provide the perfect nest or food for certain pests, we want to keep them out as best we can if our cannabis plants are to thrive. We've put together a list of the most common pests found in cannabis plants so you can learn how to quickly detect these uninvited guests.
Prevention Is Key
Before we get into the different types of pests, it is important to note that the best way to avoid them is (as always) by prevention. It is never a good idea to grow with the assumption that you can do little work and reap big harvests.
Indeed, there are methods of growing that are clean and efficient, such as hydroponics, but if we want to prevent pests there is always the minimum requirement of keeping your plants as hygienic and protected as possible. That includes cleanliness and space, maintenance of temperature and humidity, controlling airflow, and regular inspections, amongst others; all with the intention to reduce the risk of pests.
Cannabis Pests
It might be that you already have a pest problem but aren't sure who is the culprit. Many of the pests listed here are quite hard to detect in their early stages and can become a pain to deal with once they have multiplied. Usually, when the signs become noticeable the damage has already been done but there are still plenty of treatments for each case. We will not be focusing on treatments here and the purpose of this article is to identify each of the pests and their symptoms so you can be sure you're treating the right problem.
Mold
Any grower who has had to deal with mold knows it's a particularly difficult pest to keep at bay. Mold is a fungus that breaks down organic matter and feeds off the resources to reproduce. Once the conditions are ideal for them to reproduce, mold spores land and multiply rapidly as they begin to destroy everything in their path.
There are a few different kinds of mold which can affect cannabis plants at any stage of its life. The two most common examples are botrytis and powdery mildew, both of which can cause serious damage if they are not tended to immediately.
Botrytis - Botrytis is one of a cannabis grower's worst enemies. If the conditions are not corrected fast, this mega destructive fluff can turn your beautiful flowers into a horrible mush in a matter of days. Botrytis usually develops during flowering because of warm temperatures combined with a high relative humidity.
Botrytis grows as a white or grey fluffy web. It's hard to detect because very often it will start developing from within the flowers where there are trapped pockets of humid air. Leaves around the bud turn yellow and become weak enough to fall off easily. The inside of the bud tends to start rotting first as the mold works its way outwards.
Powdery Mildew - The first signs of powdery mildew can be noticed forming on the leaves, but it soon spreads over the whole plant if it is not treated. It is recognisable through the white powder it leaves behind, which creates a thin layer over the leaves that prevents them from photosynthesising properly.
The leaves on a cannabis plant that is dealing with powdery mildew start to turn yellow and brown, eventually withering and falling off as they die. Heavily affected plants start to develop black spots of the leaves. Once this happens, spores are distributed at an accelerated rate, making the fungus difficult to control without hurting the plant even further.
Aphids
Aphids are normally found crawling around in outdoor grows in spring, but they can also appear indoors. Not all of them look the same and they vary in size and colour. They like to hide under the leaves or around stems and can be identified by two physical characteristics.
Firstly, adult aphids have two thin antennas at the top of their head that are roughly half the length of their body. Secondly, on either side of the bottom end of their bodies they have tubular formations that almost look like a stump. These are called cornicles.
Aphids colonise by reproducing asexually, which means they can spread very quickly until there is a colony of egg-laying males and females. They suck the sap out of a plant for food, which can be pretty destructive once the numbers are high enough.
Symptoms include:
- Yellow, wilting leaves.
- Slow plant growth.
- Sticky excrement (honeydew).
- Sooty mold.
Fungus Gnats
Also known as soil gnats, fungus gnats become first noticeable after they emerge from the top of the soil. They appear mostly due to wet conditions from overwatering. Fungus gnats look like small flies, and they jump or run around the top soil in a distinct fashion.
Fungus gnats lay their eggs in the soil, which hatch into larvae. This is where they become most problematic because the larvae may start to feed on the roots. When the infestation gets out of control it can be devastating to a cannabis crop. Fortunately they are easy to spot and aren't a big issue if you don't wait too long before dealing with them.
Symptoms include:
- Small 'flies' hanging around the base of the main stem and on the top soil.
- Root problems shown through the leaves. That includes yellowing, browning, wilting, spots, and an overall decline in plant health.
- Growth slows down.
Thrips
Another sap sucking insect commonly found in cannabis plants are thrips. These bugs are extremely small and mate quickly, making them very hard to keep under control once they find their home in your garden. They like warm temperatures and normally favour indoor grow spaces over the outdoors. If they take over, a cannabis plant will likely show some unhappy signs and yields may be reduced if they are not sorted out.
There are many different species of thrips that can affect plants. Some have wings and others are like small worms. The most common cannabis thrip tends to be a species that flies and has black, yellow, white, or brown markings or stripes. They like to lay their eggs on cannabis leaves and will multiply multiple times per year when they are allowed to.
Symptoms include:
- Silver markings on underside of leaves.
- Brittle leaf surface.
- Drooping plants.
Leaf Miners
Leaf miners do as you would expect them to. They literally bury their eggs inside the leaves of a cannabis plant which turn into larvae that feed off vital plant tissues. The larvae dig their way through the inside of the leaves until they mature and drop out onto the top soil (or other area of the plant), turning into a pupa. Then, they develop into a flying insect which will try to reproduce and lay more eggs.
Their size makes them particularly difficult to see in the early stages of infestation. Leaf miners typically appear when the humidity and temperatures are too high. Luckily, the larvae provide some clear signs of their presence. They can establish themselves in any type of grow where the conditions are favourable. Indoors, they are slightly easier to control.
Symptoms include:
- Brown/translucent markings that look like tunnels.
- Spots or holes on leaves.
- Leaves dry out.
- Slow, wilting growth from lack of photosynthesis.
Whiteflies
The whitefly are another common pest problem in cultivation. They can be found lurking around the undersides of leaves, where they feed off the plant sap, as well as lay their eggs. White eggs are laid in a circular formation to create groups, which hatch into crawlers that go through various stages of growth before fully evolving into an adult.
Adults spend their time closer to the canopy, whereas young whiteflies can be seen in the lower areas of the plant. Adults can be described as small, moth-like insects that have yellow or white bodies. When they are not flying around, they tend to group themselves together underneath the foliage, making them easy to spot.
Symptoms include:
- White puncture spots on leaf tops.
- Leaves yellowing/dying off.
- Sticky excrement (honeydew).
- Sooty mold.
Spider Mites
Most growers have heard about spider mites and avoid them like the plague. Spider mites become super annoying to get rid of once they find their place in your grow space. Do everything you can to prevent these critters ever entering otherwise you may be at war. Spider mites are known to come back, again and again, making them extremely hard to eradicate.
Spider mites are either red (most common), white or black and are as small as a pin head (less than a millimetre). They feed off cannabis plants by sucking nutrients from cells in the leaves. The most tell tale sign of an infestation is the classic web structure they build around the flowers. However, there are some indications we can hopefully pick up on before it gets to that stage. High temperatures with low humidity are spider mites' favourite conditions.
Symptoms include:
- Fine, silky web underneath leaves and around stems.
- Heavy infestations begin to cover flowers.
- Spots on leaves.
- Stunted growth.
Cochineals
Cochineal affects many plants throughout nature. This insect crawls all over a plant in search for food, sucking out sap as it travels. They attack cannabis plants firstly around the base of the main stem and work their way upwards. Amongst the 8000 different types, there is one main species of cochineal that is particularly dangerous for cannabis.
Cottony cochineals are grey with a silky white, soft shell. They can also appear as a red or brown colour. Females lose their legs once they attach themselves to a plant, but males have wings and can fly around.
Cochineals are a nuisance to remove because they are quite hardy and resist many insecticides. Like many pests, they prefer warm temperatures where there is little moisture.
Symptoms include:
- Yellowing, dry leaves.
- Sticky residue on stems (similar to aphids and whitefly)
- Sooty mold
- Silky white egg deposits.
Nematodes
Also known as roundworms, nematodes look like tiny, tubular worms. Nematode symptoms are often confused for roots problems such as nutrient deficiency or over/underwatering. This is because they primarily attack the roots, limiting their function and eventually killing a plant if they are left alone.
There are thousands of different species of nematode, and around half of them are parasitic for plants. Although some can be beneficial, most of the time their intention is to feed off cells and other useful bacteria and fungi around the roots. Some types of nematode can also attack stems and branches, causing them to deform.
Symptoms include:
- Weak, wilting plants.
- Deformed growth.
- Yellowing leaves from root problems.
- Roots stop developing, swell and become rough.
Caterpillars
It is surprising how much a small bug can eat in one day. Caterpillars don't tend to arrive in huge numbers but just one or two in a garden can be enough to cause serious problems. Caterpillars have the ability to heavily chomp through the leaves and buds on your cannabis plants at a rapid rate. When they are still small they are not easy to see, especially if they are green.
Caterpillars grow fast when they have unlimited food available to them. The larger they get, the more they can eat, so if you notice any signs it is best to get searching as soon as possible. Normally they hide on the undersides of leaves but can be found munching almost anywhere on the plant. Leaves and buds are their prime targets.
Symptoms include:
- Missing chunks of leaves.
- Specks of faeces on leaves or stems.
- Noticeable bite marks/holes from feeding.
Slugs and Snails
Another hungry organism that has an appetite for cannabis foliage. Slugs and snails are mostly found on outdoor plants after rainy periods, however they can sometimes find their way indoors too. Outdoor gardens need protection otherwise they can be a persistent problem. Fortunately, slugs or snails are easy to notice, and leave behind some pretty compelling evidence of their doings.
Symptoms include:
- Slimy/shiny residue trails with a silvery glint.
- Bite marks on leaves.
Birds
Not your usual suspect, but birds can be unnecessarily destructive to a young cannabis plant. They may be searching for food and if you're not careful they will find and dig out seeds germinating in the ground. It is rare but it can happen that they also decide to remove some leaves from your plants too, or if the plant is small enough they may uproot it completely.
Obviously birds should not be a problem if you are growing indoors, but for those outdoor growers, one must take some precautionary measures to avoid them taking a fancy in your plants. Many growers set up reflective materials or build a scarecrow as a way to prevent birds getting interested.
Symptoms include:
- Seeds do not sprout.
- Ruined stems and leaves.
- Chunks of damaged foliage often left lying around.
Other Animals
There are plenty of other living things that can set your grow back a few steps. Wherever you live, there will always be a risk when it comes to pests entering your garden. Make sure you take all the possibilities into consideration and setup your grow space in way that minimises the chance of any pest ruining your hard work.
Any of these pests getting access could mean your plants take some fairly heavy damage. Other pests/animals you may need to watch out for:
- Cats and dogs
- Mice and rats
- Moles
- Deer
- Wild boar
- Ants (can give you an indication there is an infestation of other pests).
Conclusion
Now you are able to identify the common pests found in cannabis plants, focus on learning how to treat each of them. Having a solution ready for if a pest strikes means the problem is less likely to spread before you can do anything about it. Keep track of the environment and regularly monitor your plants so you know you're doing everything you can to prevent animals, bugs and fungus from plaguing your beautiful crops.
Pest Problems on Super Skunk by Moback66 from GrowDiaries.
If you found this article useful or have any comments to add, feel free to share your thoughts down below!
External References
Insects and Spider Mites. - Wehner, Todd & Naegele, Rachel & Myers, James & Dhillon, Narinder & Crosby, Kevin. (2020).
Nematodes: Biological Control. Gowen, Simon. (2020).
The diverse mycoflora present on dried cannabis ( Cannabis sativa L., marijuana) inflorescences in commercial production. Canadian Journal of Plant Pathology. - Punja, Zamir. (2020).
Three Botrytis Species Found Causing Gray Mold on Industrial Hemp ( Cannabis sativa ) in Oregon. - Plant Disease. Garfinkel, Andrea. (2020).
Amnesia Haze
Royal Queen Seeds
Advanced Nutrients 
BioBizz 
Shogun 
