Pests in Cannabis plants: how to prevent them

What is a pest?

In Cannabis growing, pests are all those organisms capable of harming or destructing plants. Pests that attack Cannabis plants include insects, fungi, nematodes, bacteria, and viruses, among others. Learn which are the most common pests found in Cannabis indoor crops and how to prevent them. Keep bugs off plants without pesticides!

Spider mites (insects) infestation in Cannabis plant – It’s already too late to save this bud!

Pests may be shown in Cannabis plants mostly with leaf problems and root problems, but there’s a huge array of organisms that can harm different parts of the plant. Some of the pests that affect marijuana plants can be devastating for our crops if not dealt with in time, so proper prevention of these potential threats is crucial.

Keeping a clean grow room is essential to avoid problems with your plants. Air filters, dehumidifiers, and exhaust fans are good options to keep the air fresh and clean, and humidity levels at range. Trays for collecting runoff water must be clean and collection must be done as soon as possible.

Clean and disinfect your grow tent regularly to avoid pests

Types of pests in Cannabis plants

There are hundreds or thousands of organisms that are considered pests. Some of them are insects, fungi, bacteria, viruses, caterpillars. This makes plant pests identification rather confusing at the beginning. We compiled the most common pests for Cannabis plants in indoor crops but there are many others.

Insects and bugs in marijuana plants

Insects considered pests in Cannabis crops are the ones that feed on the plant and/or secrete some substance that damages the plant, promote fungi growth or carry a disease. Growing Cannabis indoors, there’s less chance of finding random insects on your plants than growing in your garden. The problem is, when bugs get in your grow tent, they can thrive rapidly and damage your plants very quickly. That’s why monitoring for new insects periodically is key to avoiding infestations.

Sometimes you first spot signs of the presence of insects and bugs before seeing the actual insects, because they are too small or they hide from the naked eye. Always check leaves on both sides and look for white spots, dark spots, fuzzy patches, and anything not “normal”. When finding any sign of pests, act as soon as possible and get rid of them. After that, monitor your plants and environments for the following weeks.

pest damage in Cannabis plants
Cannabis plant with leaves eaten by Thrips

Some of the most common insects found in indoor Cannabis crops are thrips, fungus gnats, aphids, and spider mites. All of them attack the leaves but can be found also in the soil mix, in the water runoff if left in the trays, and even in the preflowers and buds. When looking for insects, also be aware that they can appear in the form of eggs or larvae. Mind that every region has its own set of pests and insects, but some of them are widely spread. If you are growing in a dry region, there’s less chance of finding pests and bugs and also of developing serious cases of fungi.

Pests insects: thrips
Cannabis leaves with thrips (black and white) and thrip larvae (oval-shaped white)
Thrip larvae look like small rice grains. Look for them with a hand lens!

On the other hand, some species of insects are related to the cannabis plant but not all of them are harmful. In fact, some insects are beneficial. For example, Ladybugs act as biological control because they are natural predators to pest insects, such as aphids, mites, and scales. Mind that ladybugs in their larva stage eat hundreds of aphids, so it’s ok to release or buy some adults in your crop, but giving them the time and environment to thrive and reproduce will help in the long run. This can be an effective management approach for pest control if you want a pesticide-free crop.

Pest management in Cannabis plants: lady bugs act as natural pest control
A single Ladybug in a Cannabis plant can eat hundreds of aphids, a whole family of ladybugs can eat thousands!

Earthworms are not insects, they are annelids. Earthworms are great allies to your Cannabis plants because they make the soil much more fertile and also increase the ability to retain water. Worm castings are great for Cannabis growing because they have lots of valuable nutrients and they also protect your plants from many diseases, especially if you grow organic. This natural fertilizer may be bought but you can also make your own at home. If you find earthworms living in your pots, let them thrive! They also provide aeration to the soil, which is very important for the roots to grow healthy.

Earthworms are very valuable for healthy soil and healthy plants!
Earthworms are very valuable for healthy soil and healthy plants!

Fungus in Cannabis crops

Fungus, like insects, can be harmful or beneficial to the Cannabis plants. The fungi species that are considered pests are the ones that rot, decompose and damage the Cannabis plant. They can appear in the leaves, roots, stems, and flowers. There are many species of fungi considered dangerous for the Cannabis plant from germination to the flowering stage and even after harvesting. Pythium, Fusarium, Powdery Mildew, and Botrytis are some of the fungi pests that attack most Cannabis indoor crops.

Pest management: fungi in soil mix
Fungi in grow tent – Mind that not all species of fungi look like this!

Mold is a type of fungi that grows filaments called hyphae and looks fuzzy. Some mold species considered pests are Fusarium and Botrytis. High humidity levels favor mold growth so air conditioning and dehumidifiers are good allies for indoor crops, especially in tropical regions.

Pest in Cannabis plants: fungi in leaves

Mold tends to attack strongly during the flowering stage and it can be devastating so pest control during flowering is key. White mold is one of the most common and can ruin the smell and taste of your bud very quickly. When small strains of white powder can be observed on the surface of the leaves, you are in the presence of mold. If left untreated, those spots will spread and can end up taking over the entire plant and ruining the crop. Consuming Cannabis products with mold is dangerous for your health so any parts of the plant with growing fungi must be discarded, not consumed.

Pest management: Cannabis seedling damping-off due to fungi infection (pythium)
Cannabis seedling damping-off due to fungi infection (pythium)

On the other hand, some fungi species are considered beneficial, such as Trichoderma. The term Mycorrhizal fungi refers to a symbiotic association between a plant, Cannabis in this case, and a fungus. These beneficial fungi form a mutualistic relationship with the Cannabis plant acting as a biological control agent against some fungal diseases of plants and supplying the plant with nutrients, among other benefits.

Inspection and monitoring tools for pest management

Learning how to monitor and inspect our plants is key to finding pest signals and acting quickly. Having some simple tools for making this process easier is something every grower must consider.

Hand lenses

Some pests insects are almost invisible to the naked human eye so a loupe, hand lens, or magnifying glass is very helpful to identify small insects, eggs, and larvae. You can find them in gardening, antique, or hobby shops. The same hand lenses used to check trichomes and knowing when to harvest are perfect for spotting small insects and mold before it’s too late!

Use the same hand lens for checking trichomes and pests!
Use the same hand lens for checking trichomes and pests!

Yellow and blue sticky traps

Sticky traps are cards that you can place in your grow room for attracting (and sticking) many species of insects. For some insects, only a few will get stuck and you’ll have to remove the others, but it can be a time-saver in a matter of identification. For some pests, these sticky cards are effective as a means of pest control because the insects feel very attracted to them and most of them will die stuck without having to apply insecticides.

cannabis flowering sticky traps for pests
Place yellow or blue sticky traps for pest management without pesticides

Plastic gloves

Wear Plastic gloves to manage your crop in order to avoid outside contamination.

Pest management in the flowering stage: set sticky traps and wear gloves to check your plants
Pest management in the flowering stage: set sticky traps and wear gloves to check your plants
Blue sticky trap with hundreds of thrips stuck on it after a few days. They really work!

Grow app

Grow with Jane free app works as a grow diary to log the exact time that an insect appears in your grow (with photos and notes) and the measures taken to get rid of it. You can set reminders for applying pesticides, cleaning your room, and inspecting your plants. Tracking your pest control management proves extremely helpful for knowing which methods worked in the past and replicating them. Also, helps track humidity and temperature changes in relation to pest appearance. So you’ll know that with a given set of environmental changes, some pests are prone to appear or disappear.

Download the Grow with Jane app for free and start monitoring your crop like a pro!

Grow with Jane App Home view
Grow with Jane App Home view

Prevention and management of pests in marijuana plants

The first thing you can do is to sanitize the grow room. From the tent to the pots, the tools you work with, absolutely everything must be disinfected. On the other hand, you have to check that there is no dead plant material, such as leaves that come off the plants. Many growers recommend removing the lower branches of the plant because pests tend to attack the lower parts of the plant first.

Good indoor ventilation, using low-temperature lights and dehumidifiers, and having a good exhaust fan, are very important for a healthy crop. Keeping plants healthy and fertilized is very important since pests and fungi usually attack the weakest ones. For that, control the nutrient schedules and water irrigation. Indoor crops allow us to have control over temperature and humidity, helping to prevent pests, mold, and viruses. In this linked article, we explain the perfect temperature and humidity rates for each stage of the Cannabis plant.

If some plants are already infected, isolate them if possible, taking them away from your crop until you deal with the pest. If that’s not possible, treat all the plants living in the grow room as a means of prevention.

Treating other house plants is different from treating Cannabis plants for pests because they are intended for human consumption. Consider safety in pest management to avoid health issues associated with pesticides

Good ventilation is key to achieving a pest-free crop! Small fans inside the tent help a lot.
Cutting the lower branches helps keep pest management easier and also promotes growth at the top of the plant

10 tips to avoid pests in your grow room

  1. Inspect your plants with a magnifying glass or loupe and watch for: signs of pests like spots or “dust” on the leaves, changes in color and shape of the leaves, the presence of insects, and any anomaly.
  2. Place yellow sticky traps in your grow tent to attract pests insects living in your plants and make identification easier. For some pests, it also works as a control method because some insects are naturally attracted to the color yellow.
  3. Identify the organism living in your plants and determine if it’s a pest or just an insect passing by. If it’s a pest indeed, take control measurements to keep it away from your plants.
  4. Do not overwater your plants, as this may help many species of insects and fungi to develop faster.
  5. Sterilize your grow room and every tool, tray, and shelf when using and especially between crops. Some pests may come back crop after crop if they are not dealt with on time.
  6. Keep your grow room or tent ventilated at every time and keep temperatures and humidity within acceptable levels. Keep room humidity levels below 50% in the flowering stage to avoid fungi to thrive.
  7. Use potting mix from reliable sources and sterilize if possible. Do not reuse potting mix if you’ve found pests before, just throw it away. Sometimes homemade compost contains fungi, insect eggs, or larvae that may develop later.
  8. Change clothes before working in your grow room if you’ve been outside to avoid carrying pests from outdoor crops or gardens. Sanitize your hands before touching your plants.
  9. Do not bring in plants and clones with fungi or insects on them to the grow room because they will rapidly spread to the other plants.
  10. Defoliate very bushy plants, as they attract lots of sap-sucking insects and it also makes it difficult to find some of them.

Tell us in the comments which pests are you having trouble with and which ones do you want to read articles about.

If you are having trouble with pests, download our free grow app and send us a dm. Our team of experts can help you! As a Grow with Jane member, you can access our growing community, ask questions, and show your plants!

11 thoughts on “Pests in Cannabis plants: how to prevent them”

    • Hi Messy! Thank you for your contribution! Predatory bugs are indeed extremely beneficial for fighting a thrip infestation without using chemical products! Happy growing!

  1. Tons of information but limited to indoor pests. Wish there was more on ourdoor growing as Im a seasonal, outdoor grower. That isn’t to say we have no pests LOL…far from it. Its a constant battle out here & likely deserves its own dedicated section xx

    • Hi Annette! Thanks for reading and commenting. I’m working on new articles regarding this subject. As you say, outdoor growing deserves its own section and it varies a lot between regions. I’m on it! It would be helpful to know your region and which pests are you battling right now to give the best advice on how to manage them.
      As this is an international site visited by people from many countries, we try to cover the most common issues and pests across the globe first. Stay tuned and we’ll be covering those issues soon! Happy growing!

    • Hi Crystal! The larvae in the pictures are thrip larvae, they look like a white rice grain. The picture was taken with a magnifying glass 30x so they are very tiny to the naked eye. The black dots in the same picture are thrips’ feces and the white and brown-ish bugs are the adult thrips. The leaf has white dots on it and those are the markings of the thrips bitings as they feed on the leaves. Thanks for reading and commenting!

  2. Organic ways to prevent bug infestations . What research has been done to the benefits and are there any negative side effects to consider the use of organic materials.

    1. Add used coffee grounds to the top 1 inch of the soil. Also adds nitrogen to soil.
    2. Cinnamon sprinkled on the soil surface
    3. Ripe banana skins. chopped in small pieces buried in the soil repel bugs and add.
    potassium as they start to decompose.

    • Hi Lynn, sprinkling cinnamon on the soil surface may discourage some insects like ants from going on some plants, some other bugs will just ignore it. On the other hand, any organic material not composted (like banana peels and coffee grounds) that is placed on the surface or slightly buried attracts lots of pests as it starts rotting in the soil. This can cause root rot and even kill your plants. This is a relatively common practice but studies have shown that it’s more perjudicial than beneficial in many cases, as the amount of nutrients in those grounds and peels is relatively low and the risks of pests, bugs and fungi is high. If you want to add some organic materials as fertilizers they must be composted first separated from the soil mix where plants are and only when the compost is ready and all the organic materials are composted, then you can add it to your plants for maximum benefits. You can tell that the compost is ready because no organic material rests are visible there, instead you have fresh dark soil with a distinct “earth smell”. If you see flies, whiteflies, fungus gnats or any other insect that feeds on rotten material then it’s probably not ready. Earthworms can be very beneficial in the composting process so add some to your compost to make the process faster and your compost rich on worm castings. Thanks for reading and commenting, happy growing!


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