How to get rid of powdery mildew on marijuana plants?

We have some new marijuana clones that have a gray mold on them. Is there any cure for this? It looks like a spore because it is dry and puffs up when you come into contact with it. We’ve been removing any infected leaves but nothing has really altered. The mold just keeps spreading. Aside from the leaves that have been affected, the marijuana plant is growing fine. We have a dehumidifier in the room, so it’s dry in there. Is it possible to cure this or should we just start over?

I have been cloning this particular marijuana strain for a number of years. Last year some powdery mildew infected it. I thought the environment was to blame so I sprayed the clones with some natural defense methods. When the strain was introduced to a brand new environment with more plants, the mildew came back. Can powdery mildew be infused with the marijuana plants DNA or is it just an environmental issue?

Powdery mildew is definitely your problem. The fungus attacked marijuana intermittently prior to 1999, but, after that, some strains became more aggressive. It appears more commonly in both indoor and outdoor locations. The mildew has evolved in such a way that cannabis is an acceptable source of food. The problem will get worse before it gets better as industrial hemp is allowed to grow in large volumes in Canada. Many different species of powdery mildew exist, but, as far as I know, no research has indicated which ones are going after marijuana. Powdery mildew is often white in color.

In contrast to many other molds and fungi, powdery mildew works best under moderate temperatures at around the low 70’s with 50% humidity. Unfortunately, those conditions are also ideal for growing cannabis. If you get an infection of powdery mildew, don’t blame yourself. The spore just came into contact with an area that it could thrive. The spores are travel through the air and float around until they find a prime target. Based on their sheer number, they’re going to find a good location to land. Because the spores are airborne and endemic, it’s hard to keep them from attacking. When it is cold outside during the winter, there are fewer spores because of the cold and rain and the lack of spores actually growing outside.

The DNA for powdery mildew does not and cannot combine into the plants’ DNA. Eventhough some bacteria and viruses can occasionally shift DNA patterns in some organisms, fungi and molds usually don’t. The plants showed the disease because they were actually infected again. Instead of waiting for signs of re-infection, use fungicides as prophylactics. As soon as a plant is attacked by mildew, it becomes a vector for spreading that disease. All the spores grow on the surface, and removing the plant entirely just makes the spores airborne again.

There are, of course, ways to deal with and control powdery mildew. Some of the products that have proved useful for many growers will be listed here. They are labeled for use with edible vegetables and are generally thought to be non-toxic.

AQ10 is a biogfungicide that has fungus ampelomyces quisqualis. This is considered a hyperparasite fungus that works to colonize the powdery mildew infection and kill it. The Organic Materials Review Institute (OMRI) lists it for organic crop production. It is manufactured by Ecogen, Inc.

Cinnamite has many uses for eradicating pests like mites, aphids, and even powdery mildew. It is quite effective and is composed of a cinnamon extract called cinnamaldehyde. Created by Mycotech, you can find it in a number of internet venues as well as some stores.

Milk can be used in a solution of 80% water and 20% skim milk to eliminate powdery mildew. It is highly effective and can be used over and over again to ward off any further attacks.

Neem oil comes from the Indian neem tree and works as an all-natural pesticide. It can be used against mites and insects, but it also functions as an effective fungicide and tonic. The oil benefits plant health and vigor and can be found under a number of different brand names.

Plant Shield comes with the beneficial living fungus known has tichoderma harzanum (strain T-22). The fungus creates a symbiotic relationship with the cells of the plant on the surface of the leaf. It shields the leaf from any oncoming attacks and will eliminate organisms that have already colonized the plant. It will attack molds like botrytis (gray mold), pythium, powdery mildew, fusarium wilt, and rhizoctonia. These molds go after the stems, roots, and leaves of the plants. Humans and pets are not harmed by the fungus and it is labeled as organic. It is manufactured by Bioworks, Inc.

Potassium bicarbonate, an alkaline compound, shifts the microenvironment from acidic to alkaline. Most fungi and molds like environments that are acidic, and, when potassium bicarbonate is introduced, they lose their function and their organs collapse. Brand names include Armicarb 100, KaliGreen, and Remedy.

Serenade is a fermentation product that comes from the bacterium known as bacillus subfiles. It is harmless to animals and has several methods of operation. It fights off many different fungi and molds and will compete with them for resources. The plant’s immune system (system-active resistance) is activated by the presence of this bacterium. Plants also absorb Serenade and then translocate it, increasing its effectiveness. It is manufactured by AgraQuest.

Sodium bicarbonate, commonly known as baking soda, is a lot like potassium bicarbonate in the way it’s used. It should not, however, be used a number of different times because the sodium can build up and harm the plant.

You should treat the plant with one of these products every 7 to 10 days to prevent the reappearance of mold, mildew, or fungi. If the symptoms appear and the fungus begins reproducing, the treatment is less effective.


I had the white powder mold on a plant that I had treated with an organic fungicide. That plant was harvested 2 weeks ago. Now I have another plant (Crystal) that is showing the same symptoms. So, it is in my greenhouse? I sprayed all my plants with the fungicide weeks ago. My main question: is there a strain that is powder mold resistant? I live in Oregon.

Thanks Robert. Nice to see you around :slight_smile:

I would think not. Unlike Big Ag corp, Cannabis breeders have not synthesized a strain that would be mold resistant. Best offense against mold, mildew is a clean balanced environment.

Here is Robert’s latest entry into the Plant protection market.

Bug Blaster, Mold Control, (what you are asking about), and Root Protector

I got powdery mildew once from using bamboo sticks. Never used them again and never had that problem again.