Cannabis plant disease and pests are one of the biggest problems faced when growing marijuana both indoors and out. They can cause significant damage to plants that you have put a lot of love and attention into. In this guide we will highlight some of the most common pests and diseases marijuana growers face and ways of stopping and preventing them in the first place.
Prevention is the best cure
Before we start talking about pests and diseases that can affect you marijuana plant, we should think about prevention. The best way to ensure your plants do not suffer is to make sure you do everything you can to stop infestations in the first place.
For most other plants the first thing you would do is use insecticides, however, given that in a few months you will be smoking the flowers of these plants, chemical treatments are best avoided. Instead there are some natural preventions and remedies that will help to keep your plants pest free and fit for consumption.
Don’t create a good home for pests
Fungi are an inviting food source for marijuana pests, they thrive in warm and moist conditions, therefore good air circulation and ventilation help keep the conditions ideal to combat these problems.
The theory behind companion planting is that by using other species of plant alongside your cannabis plants you can fend off any unwanted pests. Growing strong smelling herbs such as mint, basil, garlic, coriander and lavender is an excellent way to naturally deter pests.
Create a protective barrier
Soft bodied insects such as slugs, snails and caterpillars can easily be deterred by sprinkling a layer of broken sea shells, egg shells and other sharp organic matter on top of the soil around your plants. If they cannot find a clear route in they will usually just find an easier target. You can also purchase diatomaceous earth, which contains lots of sharp shards designed to cause damage to insects that attempt to cross.
Most of the time the nasty critters that invade and damage our plants come from the very same soil that we plant them in. Some growers sterilise their soil with steam to kill of any nasty pests or their eggs. For those growing organically and with living soils this is not the best option as it could damage the ecosystem that will help to keep your plants alive.
Use Beneficial bugs
It might sound strange but sometimes the best cure to a pest problem is to introduce more bugs to your plants. Most of the common cannabis pests have harmless natural predators such as ladybugs, praying mantis and lacewings that will protect your plants by killing of the damaging plant eating pests.
Use neem oil
Most pests including spider mites, aphids and white flies do not like neem oil. Mix some neem oil with water and spray this onto your plants occasionally to prevent or clear any pests away.
Use plant netting
If you are worried about larger plant eating creatures such as crickets, locusts or birds use a plant net to cover your grow. This will protect them from any larger predators.
What are the most common cannabis pests
There are thousands of species of insects that could become a pest for you to deal with, here are the most common cannabis pests that you are most likely to come across with your grow.
Spider mites on cannabis
Spider mites are the most common pest for marijuana plants and if left untreated will slowly kill your plant.
Signs of spider mites
Spider mites can be an especially tricky pest, Since they are so small and can build up a big infestation before a grower even notices a single mite. Spider Mites look like little spots and are found on the underside of leaves, leaving yellow or white spots on the top of the leaves. It is worth inspecting your plants regularly using a loupe or digital magnifying glass in order to try and identify them before they get out of hand.
Treating spider mites on cannabis
Make sure you have great airflow in your grow space as spider mites love warm humid environments. Spray neem oil solution on the affected plants to rid them of these pesky mites as well. You can find the recipe for mixing this at the end.
White flies on cannabis
White flies like spider mites are a common pest for marijuana growers. They hang out under your plants leaves sucking the nutrients out of it.
Signs of white flies
White flies are easily spotted with the naked eye. They look like little white moths and will cause white spots on the top of the leaves. Shaking your plant gently will reveal the white flies as they will fly out from under the leaves.
Treating whiteflies on cannabis
As with spider mites, neem oil solution is a tried and tested treatment to rid your plants of white flies. An alternative method is to place sticky fly traps around your grow room to catch these pests.
Fungus Gnats on cannabis
Fungus gnats look like tiny flies buzzing around cannabis plants, especially around the soil. Their larva grows in wet soil, and they often appear when the topsoil stays wet for too long between waterings.
Signs of fungus gnats
A Fungus gnat infestation can get out of control quickly so it’s important to discover this problem early and eradicate it. Look out for tiny black bugs flying around your plant and crawling on the soil. It is important to check around the base of your plant and growing medium to look out for tiny translucent larvae with black heads.
Treating fungus gnats on cannabis
To get rid of fungus gnats there are a few things you can do. Firstly you can put sticky fly traps around you plant to catch the more mature pests. Also blowing a fan to circulate the air directly over your plant will disrupt the gnats. Treating the plant with neem oil solution will kill them off. It is also best to not water your plant for a few days while you treat the infestation as these gnats love damp soil.
Aphids on cannabis
Aphids are a common problem for cannabis growers and can affect both indoor and outdoor grows. They are small black insects that cluster together on the bottom of cannabis leaves. The aphids in the image below are mature, hence their darker colour, however you can get aphids that look green or clear, these are usually the younger aphids.
Signs of aphids
Aphids are one of the easier cannabis pests to spot with the naked eye. They usually swarm plants and you will be able to see lots of tiny little black insects crawling on the underside your cannabis plants leaves. It is important to treat aphids as soon as you spot them on cannabis because they spread incredibly fast, can cause stunted growth and they secrete a sticky substance that can cause mold to grow.
Treating aphids on cannabis
Fortunately aphids are reasonably straight forward to treat, but left unchecked and they can easily destroy a cannabis plant. Soap sprays are great at killing off aphids, another natural remedy is to introduce a few ladybugs to your grow. Ladybugs are the natural predators of aphids and will quickly take the opportunity to hoover up clusters of aphids. Ladybugs are pretty harmless to cannabis too so there is no real issue with introducing a few to your grow.
Barnacle insects on cannabis
These insects get their name because they resemble the barnacles that grow on the underside of boats. They are also known as wax scales and cause similar issues to aphids. They can spread quickly and leave a sticky honeydew substance on your plants that attracts mold.
Signs of leaf barnacles
Leaf barnacles are easily noticeable with the naked eye, the are usually brown in appearance and attach themselves to the thick veins of leaves, stems and branches of cannabis plants. They may from a distance look like small brown spots but use something like a magnifying glass or even a smartphone camera to zoom in on them for a closer inspection.
Treating leaf barnacles on cannabis
Similar to aphids, ladybugs are the natural predators of leaf barnacles and so introducing them to your grow will hopefully stop the spread. You can also use soap based sprays and neem oil to kill them.
Broadmites on cannabis
Broadmites can cause real problems in a cannabis grow. Because of their tiny size they can quite easily go unnoticed until it is become quite a big infestation that they are causing noticeable issues for your plants.
Signs of broadmites
Leaves will look droopy, blistered and underwatered once infected with broadmites and because they are almost impossible to spot without a microscope the symptoms can often appear to be caused by underwatering or nutrient issues. One of the telltale signs is that the leaves will appear glossy with dark brown edges or fine brown stripes across the leaves.
Treating broadmites on cannabis
Unfortunately broadmites are notoriously tough to get rid of because they are so tiny and difficult to spot and they also lay eggs inside the plant. So you may think you have killed them off only for them to come back in a few weeks time. The best known method of ridding your cannabis plants of a broadmite infestation is using a Miticide spray such as Avid. Although if you are coming close to harvest time or in the later stages of flowering then you may be better using neem oil or employing some Neoseiulus insects which are the known predators of broadmites.
Caterpillars and inchworms on cannabis
Caterpillars and inchworms are a gardeners nightmare. Left unnoticed and they can quickly swarm an entire grow room. Caterpillars and inchworms both eat the leaves of plants and left unchecked in your grow room could quickly chow down entire plants.
Signs of caterpillars and inchworms
Fortunately despite their ability to camouflage among your plants both caterpillars and inchworms are relatively easy to spot because of their size. They leave tell tale black droppings as they go and some caterpillars create a web like next for their young.
Treating caterpillars and inchworms on cannabis
The simplest and quickest way to treat cannabis plants infested with caterpillars and inchworms is to remove them by hand. Both of these insects do not swarm in anywhere near in the numbers of aphids and broadmites where there could be thousands of tiny little critters. With caterpillars and inchworms you are more likely to get 5 – 10 per plant and they are quite big and easy to spot.
Remove as many as you can, then if it doesn’t cause too much stress for your plants, it can be helpful to defoliate a little so that any that are hiding are easier to spot. Make sure you remove any sections of web like nests as these contain the eggs and will likely hatch soon only for your cannabis grow to be infested again.
Crickets on cannabis
Like caterpillars, crickets destroy cannabis plants by feasting on them. If left unnoticed a swarm of crickets could easily ruin an entire grow. Fortunately they very rarely are an issue for indoor growers, however they outdoors they can cause problems.
Signs of crickets
Fortunately crickets are nice and big and can be easily spoted on cannabis plants. Tell tale signs of crickets are if your leaves have had clear chunks taken out of them.
Treating crickets on cannabis
Crickets are rarely a problem for cannabis growers, although depending on where you live they may be more of a problem. The easiest treatment is to remove them by hand. For any outdoor growers experiencing regular issues with insects try installing a plant netting over your cannabis plants to protect them from any unwanted critters.
Leaf miners on cannabis
Leaf miners are the tiny larvae of small flies or moths that burrow underneath the surface of the leaf and live inside the plant. They are so small they are almost impossible to detect and because they live inside they are difficult to spot until they cause damage.
Signs of leaf miners
Leaf miners are one of the most obvious cannabis pests as they leave a clear trail of where they have been that looks like a little white map on the leaf (see image above).
Treating leaf miners on cannabis
It depends upon when and where you spot the infestation. If you notice it early on and the leaf miner marks are isolated you could remove the part of the plant that has the leaf miner trails on it. You could also introduce a leaf miner predator to your grow such as a Diglyphus Isaea wasp, these will make quick work of eating up your leaf miners.
If you are not too keen on introducing a parasitic wasp to your grow you could always apply some neem oil to your plants. After a few applications you should start to notice that the leaf miners die out.
Mealy bugs on cannabis
Mealy bugs look like little white hairy wood lice. You usually find them in warm humid climates. They seem to be especially attracted to cannabis plants during the drying stage. Mealy bugs suck the sap from plants as they go which drys out and damages the plant.
Signs of mealy bugs
Mealybugs are pretty easy to spot, but they spread quickly. When mealy bugs suck up the sap of the plant they are eating, their excrement is left behind which is a sugary sticky substance called honeydew. This leaves a dark sticky appearance on the leaves and buds.
Treating mealybugs on cannabis
The easiest way to clear your plants of mealybugs is to pick them off by hand. Using neem oil and soapy solutions can also help. You can also try introducing ladybirds to your plants as the natural predator of mealybugs.
Plant hoppers on cannabis
Plant Hoppers are winged bugs that eat plant sap. They also excrete sticky honeydew and a fluffy white substance that can often be mistaken for mold. Plant hoppers are more commonly found on cannabis plants in hot humid climates.
Signs of plant hoppers
Plant hoppers are not the most destructive of cannabis pests, but they will slowly suck the sap of a plant. The signs on your plants to keep an eye out for are drying or yellowing leaves and their fluffy, white mold-like excrement that sticks to plants.
Treating plant hoppers on cannabis
Adult leaf hoppers are relatively easy to spot on cannabis plants, however their young look like tiny crabs and can be more difficult to spot. To get rid of them soapy sprays and neem oil do work and predator insects also work well.
Thrips on cannabis
Thrips are tiny insects that damage the leaves of a plant. They can be dark, yellow or even clear in appearance. Without early treatment they will spread quickly and can cause damage to the foliage and overall health of a cannabis plant.
Signs of thrips
Thrips are tiny and hard to spot until there are so many of them it has become a problem. They will damage the foliage of a plant by sucking sap out of it, this leaves dry yellow patches on the leaves.
Treating thrips on cannabis
Thrips are best treated with soapy water and neem oil. However the most effective method is to introduce a Amblyseius Cucumeris. These are mites that are the natural predators of thrips, feeding on their larvae and eggs. You can purchase sachets of these predators online that you can simply sprinkle onto the plant. These predators do not feed on adult thrips but instead work by breaking the life cycle by feeding on the young. For larger infestations you can also introduce Orius too which will feed on adult thrips.
Slugs and snails on cannabis
Slugs and snails are probably one of the most common pests for cannabis growers and although they are slow movers they can eat surprisingly fast. Left untreated and a slug infestation can quickly ruin an entire crop.
Signs of slugs
Again slugs are pretty easy to spot, they also leave a shiny trail wherever they go and will eat large sections of leaves leaving clear damage marks.
Treating slugs and snails on cannabis
Slugs are easily found if you inspect your plants closely enough. The quickest way to get rid of them is to remove them by hand. Don’t use salt to kill them though. Although salt will do the trick it can be damaging to your plants and if too much seeps into the soil it could kill them too.
Instead a natural way to prevent soft bodied insects such as snails and slugs from reaching your plants is to have a layer of sharp, spikey barriers such as broken sea shells, crushed eggs shells or pine needles around the edges of your plants.