White Spots On Cannabis Leaves: Cause & Prevention

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Growing cannabis can be a whole lot of fun, and quite rewarding too. With that being said, cannabis plants are susceptible to a variety of pests and diseases.

There are many things that can kill your cannabis plants. if you see that there are white spots on your cannabis leaves, then you have some problems.

White spots on cannabis leaves are generally caused by a fungal disease, known as white powdery mildew. There are also a variety of pests such as Aphids and Spider Mites that can be responsible for this occurrence. Here is a helpful guide on the common causes, prevention, and the best ways to treat your plant leaves.

white spots on cannabis leaves


What Causes White Spots On Cannabis Leaves?

There are two main things that will cause white spots to occur on your cannabis leaves. The first is a fungal disease known as mildew, and the second is a variety of pests.

Let’s take a quick look at both of these issues right now to see exactly what they entail.

Fungal Disease

The most common reason for white spots appearing on your cannabis plants is due to a fungal disease. To be specific, this fungal diseases mildew, or specifically, white powdery mildew, also known as WPM.

In the early stages of a white powdery mildew infection, white spots will appear on the leaves of your cannabis plants. The leaves most affected are usually the lower leaves.

If you catch this early, you may be able to do something about it. Generally speaking, as the white powdery mildew spreads, the spots will get much larger, and turn into big circles.

The mold will then spread to other parts of the plants, and this then becomes very hard to deal with. What you do need to be aware of is that fungus spores are in the air all around us.

It’s not like you brought those spores in with your soil, or on your clothes. Fungus and mold spores are in the air all around us. However, it’s the conditions in which you how’s your plants that will determine whether or not that mold ever gets the chance to grow.

In terms of recognizing a white powdery mildew infection, the first thing to look for is actually insects. If there are no insects present, and you have white spots, then it is most likely a white powdery mildew problem.

In terms of appearance, these spots look like fuzzy circles on the leaves of your plants. Keep in mind that here you are looking for white spots, but if you have brown or yellow spots, then there is a different problem.

there are many things that can cause a white powdery mildew infection to take hold. For one, if your plants do not have lot of air circulation, then this mildew can take hold.

Moreover, mildew likes low light conditions, so if your plants don’t get enough light, this can be another cause. Also keep in mind that very high humidity levels are ideal for mildew such as this to grow.

In terms of humidity, what is interesting to note is that this mildew does like high humidity levels, but at the same time, it also likes a very dry growing area. If your soil is very dry, but the air is very humid, it makes for a perfect climate for this mildew to grow.

What also needs to be said is that white powdery mildew tends to really like newer plants rather than older plants. Moreover, fertilizing your plants way too much can also cause this to occur.

White powdery mildew can feed on fertilizer, at least to a certain extent. This white powdery mildew will eventually kill your plants.


The other thing that may be causing these white spots to appear on your cannabis leaves is pests.

If you see that those little white spots are moving around, then you definitely have a pest infection. One of the most common cannabis pests here is known as the whitefly, also known as a type of aphid.

Aphids will feed on your plant’s leaves, and they look like very small white moths. These pests also lay eggs, and they can lay up to 300 eggs at once, and yes, these look like little white dots.

Keep in mind that these little flies or aphids usually hide on the underside of the leaves, which is also where they lay their eggs. If you have a whitefly infestation, and your plant is starting to dry and yellow, it is a sign that the infestation is in its later stages.

The other common pest that can cause these white spots to appear are spider mites. Spider mites also feed on your plant. However, spider mites themselves are reddish-brown in color. Yet, the eggs they lay are white.

Now, when it comes to spider mites, when they eat the plant, they can leave little white circles behind. So, as far as spider mites are concerned, if you see white dots, they could be the damage left behind by the mites, or they could be the spider mite eggs.

If you see little brown and red creatures, those are spider mites, and the white dots are their eggs.

How To Prevent White Powdery Mildew

As mentioned before, these fungus spores are present in the air all around us. With that being said, there are a variety of things that you can do to prevent this white powdery mildew from taking hold.

Let’s take a quick look at all of the things that you can do to prevent white powdery mildew from killing your cannabis plants.

  • Keeping humidity levels at an ideal level will help prevent mold spores from taking hold and spreading. Ideally, to prevent mold spores from spreading, you want the humidity level in the grow space to be at 40% or less. However, some plants require higher humidity levels, which is why you also need to pay attention to the other tips we have to provide you with here.
  • One very simple way to prevent white powdery mildew from occurring is to get a mold resistant strain of cannabis.
  • Yet another thing that is going to help prevent white powdery mold from occurring is by properly spacing out your plants. If plant leaves touch each other, and if the plants are too crowded in general, there won’t be enough air circulation present. If there is not enough air circulation present, those mold spores won’t be able to leave the grow space. They will just keep building up in your grow space. Moreover, having good air flow will also help to decrease humidity levels by forcing moisture out of the grow space.
  • On that same note, having very low air quality can also help to spread white powdery mildew spores. Therefore, having a decent air purification system can prevent this from occurring. An air purifier will remove those mold spores from the air.
  • As mentioned before, mold likes when the soil is very dry, but the air is humid, so something you can do here is to ensure that your plans are properly watered at all times. Make sure that your soil is never too dry.
  • Mold does like low light conditions, so a good way to prevent it from taking hold is by ensuring that all of your plants get more than enough light. getting enough light is of course also very important for your plant’s growth in general.
  • White powdery mildew also tends to do very well when the soil is way too over fertilized. Therefore, make sure to not use too much fertilizer in your soil.

How To Prevent Pests On Your Weed Plants

The fact of the matter is that preventing pests from occurring on your cannabis plants is much harder than preventing mildew.

However, the following tips will help prevent pests from infesting your cannabis grow space. Nothing here is surefire, but every little bit helps.

  • You want your grow space to be completely sealed from the outside world. Make sure that all doors, cracks, and everything else is perfectly sealed so that nothing can get in. Bugs coming in from the outside is very common.
  • You also want to keep all other animals out of the grow area. Pests can be hitchhikers on your dogs and cats, and get into your grow space that way. On that same note, you should also limit the amount of people that go into your grow space. The less people go into your grow space, the lower the chances of pests coming in with them.
  • Whenever you are working with your plants, always make sure that all of your tools and equipment are perfectly sterile. All tools and containers should be sterilized before use, and you should always wash your hands before handling plants. Moreover, all debris and dead plant matter should be removed right away. Whenever you plant a new plant, always use new soil and grow media.
  • If you want to take things one step further, you can always wear new clothes whenever you enter your grow room.
  • What can also help prevent pests from taking hold of your plants is by having great airflow. A bit of wind goes a long way in keeping pests at bay, because bugs usually don’t like strong drafts. They won’t be able to land on the leaves very well, and laying eggs will be a challenge too.

Related: Sprayers and Foggers for Spider Mites.

Best Ways to Treat White Spots On Your Cannabis Leaves

How to deal with white spots on your cannabis leaves really depends on what the underlying problem is.

How to Deal with White Powdery Mildew

There are a number of things that you can do in order to remove white powdery mildew from your plants. Add a tablespoon of liquid soap to a gallon of water, and then spray your plants down with this mixture.

Another thing that can help remove white powdery mildew from plants is by using mouthwash. Mix one part mouthwash with three parts water, and then spray your plants with this.

On that same note, you can also mix one part milk with three parts water, and then spray the plants with this. For one reason or another, milk seems to be a good way to kill this mildew.

Of course, if you have the money to spend, then investing in some good old fungus side will do the trick as well.

How to Deal with Pests

Pests tend to be quite resilient and can be hard to deal with period however, the easiest way to deal with pests on your marijuana plant is by using a variety of insecticidal soaps.

Increasing the airflow in the grow room will also help, but if an infestation has already taken hold, it won’t get rid of the bugs. Insecticidal soap, or something like neem oil, is the only thing that you can use to get rid of these pests.

Should I Remove Leaves With Powdery Mildew?

Yes, you absolutely want to remove all affected leaves. The more mold and mold spores are present, the faster and the bigger they will grow. Immediately remove and discard all parts of the plant that have white powdery mildew on them.

There you have it folks, everything you need to know about why your plant has white spots on it, what the causes are, and what the solutions are, the best type of treatment is prevention.


My passion for the sticky icky started nearly a decade ago, and it all began when I first laid my eyes on the beauty that is the marijuana plant.

I cover all aspects of growing from equipment recommendations to plant health/care tips to help both new and experienced growers.