Cannabis Pests and Diseases

cannabis pests and diseases

Cannabis pests and diseases are one of the biggest problems faced when growing weed, both indoors and outside. They can cause significant damage to plants that you have put a lot of love and attention into, even ruining your entire crop. In this guide, we will highlight some of the most common pests and diseases cannabis growers face, and how to deal with them. As well as what you can do to prevent them from invading your grow in the first place.


Before we start talking about cannabis pests and diseases that can affect your 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 ensuring good air circulation and ventilation will help keep the conditions ideal to combat these problems.


Aphids on a marijuana leaf

Arguably the most common of all pests to arise when cultivating marijuana, aphids feed on the juices contained in cannabis leaves. This can then cause the leaves to turn yellow and wilt, due to excessive stress. If left untreated, an infestation of aphids can stunt your plant’s growth and have a major effect on the overall quality and quantity of your harvest.

What to look out for?

Aphids are small, oval-shaped insects that come in a wide range of colors, depending on their stage of life. They can appear, white, green, yellow, black, or brown. Often found on stems or the undersides of leaves in large colonies, they are fairly easy to spot. 

Another issue with having an infestation of aphids is that they produce large amounts of a sweet substance known as “Honeydew”. Honeydew comes with its own issues. The sugary liquid waste attracts a fungus called sooty mold. Sooty Mold not only discolors and turns the affected area black, hindering the plant but also makes it unsafe to smoke. And if that wasn’t enough, honeydew is also known to attract ants, just to add to your problems.


If you spot aphids on your plant, the best thing to do is first remove all the affected leaves. You can then use homemade insecticides and soap sprays, as well as neem oil to attack the aphids. Another way to deal with these pests is to introduce ladybugs into your grow space. The ladybugs will feed on the aphids, and hopefully eradicate them.


Thrip infested leaf

Another sap-sucking pest to invade cannabis plants everywhere are thrips. These small, fast-moving insects pierce cannabis leaves with their mouths and suck out all the good stuff.

What to look out for?

A sign that thrips are present on your plants is the light-colored patches that remain on the leaves following thrip damage. Thrips can also carry viruses that affect cannabis plants. If they puncture the plant multiple times, your plant can easily get infected and die. On top of this, thrips reproduce in the tissue of the stems, leaves, and even the flowers, causing damage to every part of your cannabis plant.


The best treatment when it comes to thrips is to spray insecticidal soaps or neem oil on your plant. Again, like aphids, you can introduce natural predators to your growing space. In the case of thrips, using predatory mites works well to combat them.

Spider Mites

Spider mites on cannabis leaf

Spider mites are another common pest for cannabis plants, and if left untreated will slowly kill your plant.

What to look out for?

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 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 a neem oil solution at the bottom of this article.

White Flies

White flies on cannabis leaf

Whiteflies, like spider mites, are a common pest for marijuana growers to deal with. They hang out under your plant’s leaves, sucking the nutrients out of them.

What to look out for?

Whiteflies 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 when disturbed.


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 Gnat on leaf

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 out for?

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 for any tiny, translucent larvae with blackheads.


To get rid of fungus gnats there are a few things you can do. Firstly you can put sticky fly traps around your 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.

Bud Rot

Cannabis flower with bud rot

Bud Rot is one of the most devastating fungal diseases to affect marijuana plants. It is so harmful that it can kill off your entire crop within a week.

What to look out for?

During 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, eventually causing them to weaken and fall. The infected bud will generally start to show a white mold, which will turn gray and eventually black. The 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

Root rot disease

Root rot is caused by a lack of oxygen being supplied to the roots either by over-watering 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 plant.

What to look out for?

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


Root rot can be difficult to treat, so a lot of growers will scrap the plant and go again. 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 it. 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 on cannabis leaf

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 too close together.

What to look out for?

Powdery mildew starts as small white spots on the top of leaves, progressing to 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 grow and are not placed too closely together. Again like with most disease prevention, making sure your grow area is clean and not too humid is imperative. When powdery mildew is present, one remedy that can be used is 2 teaspoons of apple cider vinegar mixed with one liter of water. Spray this mixture onto your plants to kill the powdery mildew growth and prevent any more from cropping up.

How to make Neem oil solution

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 another detergent
  • 1 liter of warm water

Mix everything thoroughly, then pour it into a spray bottle so you can mist your plants evenly. To make a more concentrated dose, double the volume of both the neem oil and the detergent.

After spending your money on high-quality seeds, and nurturing your plant through its growth, the last thing you want is for it to be ruined by pests and diseases. Cannabis pests and diseases can differ in seriousness, with some easier to eradicate than others. Prevention is always the best way to try and combat any issues. However, sometimes these things just happen. Hopefully, you now feel a lot more informed on what to look out for, when it comes to pests and diseases. And how to deal with them, should they arise. Happy growing!

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