cannabis pest control

How can farmers protect their cannabis plants from pests?

Cannabis farmers often have to face the mercy of a number of exterior factors damaging their crops – so, how can they protect their plants from pests?

Problems that can impact cannabis plants include issues such as the ambient climate and acute weather events, soil quality, insects and other pests, which can consume and contaminate the crop, including mites, aphids, flies, worms, fungi, mould and pathogens – and even some opportunistic mammals, such as rodents and deer. So, how can cannabis farmers protect their crops from pests?

Medical Cannabis Network explores the benefits and drawbacks of key pest control techniques for cannabis cultivation.

Chemical insecticides

Chemical treatments are ostensibly the fastest and most effective way to protect a valuable cannabis crop from destructive pests, acting swiftly and decisively to destroy and deter interlopers.

However, as with any other agrifood product, cannabis which is produced with the aid of pesticides must be thoroughly cleaned before sale in order to protect the consumer from any residual toxicity. The risk of pesticide residue is particularly pressing in cannabis production because, while several chemical pesticides have been nominally approved for use on edible plants, many cannabis users prefer to smoke their product – and the burning and inhalation of residual pesticide chemicals may be substantially more deleterious to the user’s health.

The varying legality of cannabis around the world is another key factor affecting the safety of chemical pesticide use, for two main reasons: firstly, in states and regions where cannabis cultivation or consumption is not legal, its illicit status acts as a barrier to comprehensive research. If scientists are not permitted by law to study the potential effects and toxicity risks of chemicals which are used to treat cannabis, then even once the drug is legalised, the ensuing lack of a reliable evidence base means cultivators and producers are not best informed as to how to safeguard their customers. In the US, for example, the Environmental Protection Agency – which oversees and regulated the use of pesticides in agriculture – did not issue official approval for any pesticide in cannabis or hemp farming until December 2019.

The lack of oversight occasioned by heavy-handed research regulation leads in turn to the second safety issue: without sufficient data or guidance to determine what methods of pest control are the safest, cultivators typically opt for either the strongest or the cheapest chemical treatment available. Some of these chemical-based pesticides are not indicated for use on foodstuffs or consumable goods; some are potentially toxic or carcinogenic. A prevailing lack of education and awareness, combined with misplaced cost-cutting measures, mean some of the pesticides used in certain cannabis cultivation operations are designed solely for use on ornamental plants.

Where cannabis farming is subject to either prohibition or strict licensing for outdoor growers, indoor farmers commonly find that the climate and ambient humidity of indoor operations act as a breeding ground for insects and fungi. However, where indoor growers respond to an infestation by deploying increased quantities of chemical treatments, they may then find that the enclosed space contributes to excessive residue remaining on the plants after harvest.

Organic insecticides

Natural insecticides derived from organic compounds or plant extracts carry less overall risk of harm to the end consumer – although, as many natural and organic pesticide treatments are still toxic to humans, extensive care should still be taken to remove any residue from the final product and farmers should take the appropriate protective measures to ensure they do not inadvertently consume traces of the treatment.

Pesticides rooted in nature include:
  • Pyrethins, whose active ingredient is extracted from chrysanthemums. Chrysanthemum oil has been in use in horticulture for centuries as a natural pest deterrent, as it has a relatively low toxicity when consumed by humans;
  • Azadirachtin, a popular active component in natural and organic pesticides, which is derived from neem oil. Azadirachtin both arrests the ability of pest insects to grow and moult; and prevents them from laying eggs; and
  • Plant extracts, ranging from garlic and cayenne pepper to rosemary and cinnamon.Treating cannabis crops with individual or mixed plant oils to destroy or dissuade pests can shore up a product’s ‘organic integrity’ and is possibly the approach least likely to harm the consumer.

Beneficial insects

These are insects which feed on agricultural pests without themselves disturbing the plants: beneficial insects do not feed on the plants, nor do they leave behind harmful residue. Depending on the species, they may focus on one or two specific pests or on several. However, they typically cannot be deployed to address issues stemming from moulds or fungi; and are not effective in deterring rodents or other mammals.

Ladybirds are possibly the most popular beneficial insects used in the production of cannabis: aside from thriving in a variety of climates, these carnivorous insects can eat thousands of aphids, mites, thrips and other pest insects over their lifetime. Predatory nematodes, which live primarily in soil, are particularly effective in consuming the eggs or larvae of a variety of pest insects. Predatory mites, which feed on spider mites, are considered exceptionally effective in eliminating spider mite infestations, particularly in the early stages of an outbreak.

This article appeared in the second issue of Medical Cannabis Network which is out now. Click here to get your free subscription today.

Cannabis farmers often have to face the mercy of a number of exterior factors damaging their crops – so how can they protect their plants from pests?

Pests, Bugs & Viruses

Unfortunately, bugs and other garden pests can totally mess up your marijuana harvest!

This page aims to be a comprehensive resource on the different types of bugs / pests / mold that can affect your marijuana crop, along with tips for preventing and solving each problem.

Pests that can affect your marijuana plants include aphids, fungus gnats, thrips, green flies, black flies, mosaic virus, spider mites, caterpillars, inchworms, whiteflies, white powdery mildew / white powdery mold, stem rot, and even mammals such as deer or cats!

If you want a list of safe, all-natural pesticides that can get rid of most of the pests on this list, check out this page:

It’s time to fight back against cannabis bugs, mold and pests!

Quick Tip! Whenever you spray plants with anything, make sure to get the undersides of the leaves too, as this is where many pests like to hang out! A one-hand pressure sprayer / mister is also really helpful for spraying leaves.

Aphids live under leaves & have different forms depending on their stage of life

Barnacles / Scale Insects
These bugs that look like barnacles and stick to the plant on stems and underneath leaves

Broad Mites
These mites are so small you will likely never see them even under a magnifier. However, you can tell your plant has been infected because your new leaves will be blistered, twisted and glossy. The overall plant will also be growing poorly and if it’s flowering the buds may turn brown. Broad mites are often mistaken for other problems like nutrient deficiencies, heat stress or pH problems.

Bud Rot or Mold
When bud rot strikes, certain buds may start looking sickly overnight, with leaves turning yellow and/or bud becoming discolored. When opened up the inside of the bud is dead or moldy.

Caterpillars, Inchworms & Cabbage Loopers
Caterpillars and worms eat holes in leaves and leave droppings that look like black specks

“Regular” crickets will munch on your leaves while “mole crickets” can tunnel under your plants and disturb their roots!

Mole Cricket – these can tunnel under your cannabis plants like moles

Fungus Gnats
Fungus gnats look like tiny dark flies. They hang around soil that stays wet for long periods of time, and their worm-like larvae crawl around in the wet top soil. Plants start getting sick if a gnat infestation gets out of control.

You’ve probably seen these before, but these seemingly harmless garden creatures will happily eat your cannabis leaves!

These bugs come in almost every color known to man so sometimes it can be tough to tell what they are just from looking. However, they all make clusters of spots on your leaves where they’ve sucked out all the sap, so if you see spots like this you know you’ve got leafhoppers!

Leaf Miners
Leaf miners are larva that actually live inside your leaves and tunnel through them to eat!

Leaf Septoria / Yellow Leaf Spot
This fungus causes round yellow or brown spots, with symptoms often starting on lower parts of the plant

These tiny white bugs look “hairy” and are found crawling on leaves and buds

Each species looks quite a bit different as an adult. Some look like pretty leaves. As youngsters, they create white and fuzzy patches that look like cotton on their butts and on your plants. Planthoppers suck the life out of cannabis plants if they start a colony.

Root Rot
Root rot is a common problem in hydroponic systems though overwatered plants in containers often display similar symptoms. Plants with root rot wilt and leaves may become discolored. In the reservoir the roots turn brown, smelly and slimy.

Russet mites are so small you can only see them with a magnifier unless there are thousands of them infesting your plant. They live the the crevices of leaves, stems or buds.

Slugs / Snails
Slugs and snails usually come out at night, leaving holes in leaves with scalloped edges from their individual bite marks. They also leave slime trails on leaves and on the ground.

Spider Mites
Spider mites are often caught from another grow room, and their bites leave small white speckles all over your leaves. They’re so small they can be hard to see, though the best place to look is underneath leaves. You may see webbing if there are enough of them living on the plant.

​ Thrips leave irregular bronze or silver marks that may look like “dried spit” or tiny snail trails. Their young look like fat, tiny worms.

Tobacco Mosaic Virus
It’s not known whether mosaic virus has jumped from tobacco to cannabis plants, but in this article I’ll share what I’ve learned so far…

Whiteflies/ White fly
Whiteflies look like tiny white moths and hang out under your cannabis leaves

White Powdery Mold
WPM leaves a white powdery substance that looks like flour or powder on leaves and stems

This easy picture guide will help you quickly diagnose your sick plants. Learn how to get rid of the most common marijuana pests!