• Post last modified:October 10, 2021
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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.


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 these things from happening. Good hygiene is key, make sure your grow room is clean and you wash your hands before touching your plants.

​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.

Spider Mites

Spider mites are the most common pest for marijuana plants and if left untreated will slowly kill your plant.

What to look for?

cannabis plant pests spider mitesSpider 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.


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

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.

What to look for?

how to prevent white fliesWhite 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.


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

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.

What to look for?

how to prevent fungus gnatsA 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.


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.

Cannabis plant disease

There is nothing more demoralising than spending months of hard work germinating and cultivating your cannabis plants only to realise that they have a disease during the flowering stage, if left this can mean that the entire grow is wasted. However there are lots of ways you can mitigate the risks such as choosing a strain that is resistant to cannabis plant disease such as Cheese. There are also lots of ways to treat these marijuana diseases once they have begun to infect your cannabis plants.

Bud rot

Bud rot is one of the most common and devastating marijuana diseases that can affect your plants. It is so harmful that it can kill of your entire crop within a week if left untreated.

What to look for?

cannabis plant diseaseDuring the first signs of bud rot the leaves at the base of the bud will begin to turn yellow. Bud rot typically starts at the youngest stems in your marijuana plants, specifically where the plant meets the soil. It softens the stems and turns them brown in color, eventually causing them to weaken and fall. The infected bud will generally start to show a white mold, which will turn grey and eventually black. Collapse of the bud will coincide with the darkened appearance and it will be reduced to a mushy mess.


To treat bud rot you should cut away the affected areas. Ensure that you keep the temperature of your grow room high, but with humidity under 50%. Make sure there is good ventilation and air circulation as well.

Root Rot

marijuana diseasesRoot rot is another terrible but common cannabis plant disease that is caused by a lack of oxygen being supplied to the roots either by overwatering or supplying them with un-aerated water.  It will affect the plant’s growth, making it unable to feed and transfer nutrients to the rest of the plan.

What to look for?

The first sign of root rot is usually wilting or drooping. However you may also notice the roots turn pale brown before darkening. Growth of your plant will dramatically slow down as well.


Root rot can be difficult to treat so a lot of growers will scrap the plant and go again. In order to stop root rot It is important to use a growing medium that has good water drainage, but be sure you are not over watering the plant. To check when it needs water, stick your finger about an inch into the soil, if it still feels damp then you don’t need to water. Only if it’s feeling dry should you top it up. It’s also vital to keep your growing medium clean. This means any dead leaves or other types of plant debris need to be removed from your grow area.

Powdery Mildew

Powdery mildew comes from lots of different fungi. In extreme cases it can kill your plant. It is caused by high humidity levels and poor light penetration usually stemming from  having plants placed to close together.

What to look for?

This cannabis plant disease can begin completely unnoticed because it starts off as small white spots on the top of leaves, quickly progressing into a pale powder on the leaves, shoots, and stems. As it progresses leaves start to yellow and the growth of the plant begins to slow.


To prevent powdery mildew you should ensure that your plants have enough room to themselves and are not placed to closely together. Again like with most disease

prevention, making sure you grow area is clean and not to humid is imperative. When powdery mildew is present one remedy that can be used is 2 teaspoons of apple cider vinegar mixed with one litre of water. Spray this mixture onto your plants to kill the powdery mildew growth and prevent any more from cropping up.

Making a Cannabis plant disease prevention concentrate

To make a neem oil solution to spray on your plants you can either mix it in a dilute format as a preventative measure, or as a more concentrated solution if you already have an insect infestation.

5 ml (1 tsp) neem oil. Always use the most natural format you can. Not mixed with any other essential oils and it should always be cold pressed.
1-2 ml (1/3 tsp) insecticidal soap or other detergent
1 litre of warm water

Mix them together thoroughly and put in a spray bottle so you can mist it evenly over your plants. To make a more concentration dose, double the volume of both the neem oil and the detergent.

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