White Powdery Mildew

White powdery mildew is a very common type of fungus (fungal disease to be precisely) found on many plants. Other names are White powdery mold or “WPM”.  Compared to other types of fungus, this one is easy to recognize and treat. However if nothing is being done about it, it can be pretty persistent and turn in to a catastrophe for your plants.

So just like other pests, it’s important to act quickly once the first signs are visible. “WPM” is known as a minor problem and only able to survive in certain circumstances, so one part of treating it is by changin the climate/circumstances in your growroom.


In this article:


How to recognize “WPM”?

Compared to other type of fungus, WPM is pretty easy to recognize. If you think about it, it’s already in the name. WPM is visible as white fungal growth starting on the leafs. It looks like a layer of white flour/dust was being poured on the leafs. WPM starts with small spots on and under the leafs, however if nothing is being done about it, it will spread fairly quickly to other leafs and eventually the buds.

This “white dust” comes in different phases. At first you have to look very close as it’s just a very thin layer, but later it it will get thicker and way more visible. To give you an idea of this whe have listed the following pictures:

WPM does not appear on every part of the plant at the same time. As you can see, it starts on specific spots before spreading all over the plant.
After it has spread,a thin layer of WPM “dust”will spread over the leafs. This means you have a true infestation and action is required!If you wait a little longer before treating a WPM infestation, the layer gets thicker and the white glow is getting more visible. Now is the time to start acting!

If there is no treatment going on and you keep waiting, these layers will get thicker and the WPM will spread over new parts of the plant. This means that your plant isn’t able to do proper photosynthesis and eventually dies. Just like other types of fungus, You have to act quickly!


What causes “WPM”?

The cause for most fungal pests is all about the environmental circumstances in your growroom/area. This is also the case for White Powdery Mildew. Next to that, a plant needs to get infected by a fungal spore before WPM can start to grow and evolve. These spores are flying trough the air (coming from other WPM contaminated plants) and eventually lands on your plant. Sometimes humans or animals contaminate a plant by carrying the spores in their clothes/fur.

Environmental circumstances

After one of these spores have landed on your plant, it needs a perfect environment to grow and spread around. These circumstances are pretty similair to the ones that other types of fungus needs to survive:

Humidity

Most types of fungus love water and need it to survive. Even a too high humidity can be enough for WPM to thrive on. Sometimes this cause problems in the vegetative phase as young plants also like a higher humidity (40%-60%). Lowering hte humidity can be done by offering a good air circulation/fans or using a de-humidifier. Once the plants are flowering, make sure to lower ht ehumidity to avoid all kind of fungal pests.

Bad Air circulation

White powdery mildew hates windy places and find it hard to settle in an area where the air is being “moved” a lot. It needs a very low air flow to settle and grow on the leafs. So even if your humidity is high, there is a small chance WPM will strike your plants if there is a strong breeze of air going through your growroom. A few fans pointing on your plants can do the trick.

No Ventilation

Spores of WPM need to reach your plants first before it’s able to settle and grow on the leafs of your plant. If your growroom isn’t ventilated enough, these spores will keep floating through the room and have lot’s of chance to land on your plant. By refreshing your the air all the time your reduce the chance of a WPM infection.

Too much leafs/ Leaf-on-leaf contact

Bushy plants with lots of leafs and branches will have a bigger chance of getting infected with WPM. This is because eventually, leafs will touch and overlap each other which attracts and collect moisture in the touching areas. If you know what you are doing, you might be able to defoliate some of the overlapping leafs. This will increase the chance of a fungal infection big time! When defoliating correctly, you could increase the final yield because the plant will focus on it’s growth and put energy in to the buds instead of keeping all leafs alive.

So the combination of WPM spores landing on your plant (by air or human/animal contact) and these kind of circumstances is the cause White Powdery Mildew growing on your plants!


In the blooming phase, its important to avoid a WPM infestation. Once it spreads and take over developing buds, its very hard to get it off and the infected buds will be useless.

How to treat “WPM”?

Treating WPM is not very hard compared to other pests. It requires some knowledge and you need to track it down before it spreads and take over your plant. We have learned that WPM requires pretty specific environmental circumstances, so that the first step to look at when treating WPM.

By changing the environmental circumstances of your growroom/area (after a WPM infection), you take away the requirements that WPM needs to survive. You can do this by:

  • Adding some fans to the growroom to offer a proper air circulation.
  • Increase the ventilation of fresh air by expanding the entrance/exit hole or getting a stronger suction fan
  • Defoliating big and bushy plants/leafs to create a better stream of fresh air through the plant and decrease humidity.
  • Lower the humidity by increasing the ventilation, or adding a dehumidfier
  • Carefully removing the WPM from the plant/leafs

Even after you created the perfect environment and removed the excisting WPM, it’s almost impossible to avoid WPM spores landing on your plant. They are in the air and will always find a way. Once the environment changes slightly in favour of the WPM (for any reason) It will quickly return and your back to start.

So next to offering the right envrionment, you could use some kind of remedy to treat and fully eliminate the fungal infection:

Always make sure that you are using the right/safe stuff so you don’t damage your plants or yourself by using toxic chemicals. We recommend the following products:

Lost coast plant therapy- Safe for cannabis and works with multiple Pests


Growsafe- Organic pesticide that works on multiple pests and is safe for cannabis consumption


Do you have more tips on how to recognize and treat White Powdery Mildew? Leave them in the comments below!