Identify, Avoid, and Treat Powdery Mildew on your Cannabis

powdery mildew cannabis

It’s a beautiful day in your grow room. You’ve long since studied up cannabis powdery mildewon the best practices for growing marijuana, your plants are blooming, and several are even approaching harvest. You check on those plants first. Perfect, perfect, perf- wait a minute. What’s that white stuff on the leaves? A quick search on the internet confirms your fears: your cannabis crop has been infected by powdery mildew.

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What is powdery mildew?

Powdery mildew comes from a variety of different fungi and can be transported through the air, ventilation systems, or by clinging to any sort of moving object (think clothing, pets, birds, etc.). The spores can remain dormant until optimal environmental conditions have been reached, which is when they begin to grow and spread. At this stage, powdery mildew will begin to look like fuzzy patches of flour or sand and will most likely be found on the leaves of your cannabis plant.

Once it begins to grow on the leaves of a marijuana plant, powdery mildew can spread to the stem and buds. This fungus hinders the plant’s photosynthesis process, and, if left untreated, will ultimately kill the entire plant and ruin that plant’s harvest.

Optimal conditions for the growth of powdery mildew occur in areas of high humidity (usually above 55%) combined with poor ventilation and little airflow. Once growing, it can spread from plant to plant through the air or, more easily, across leaves that are touching.

How can growers avoid it?

The best way to avoid a powdery mildew infection is to grow your cannabis crop in an environment that is not conducive to the mildew’s growth. If possible, ensure that the following conditions are present in your grow room:

Maintain a temperature between 72-75 degrees Fahrenheit
Try to keep the humidity below 48%
Increase airflow and ventilation Water plants during lighted hours to encourage evaporation of leftover moisture
Avoid physical contact between cannabis plants
Invest in plants that are resistant to diseases or infections
Sterilize vents, fans, and ducts on a regular basis
Disinfect tools and clothes that may be carrying spores
Check your cannabis plants’ leaves regularly for early signs of powdery mildew

How can growers treat it?

Powdery mildew
Photo By: AJCespedes /
A highly recommended approach to fighting powdery mildew is to remove the affected leaves. This should be the first step in treating the mildew, as it can quickly and easily spread to different parts of an infected cannabis plant and between neighboring plants. Growers should use a damp paper towel to carefully grasp the infected leaves and place them in a plastic bag.

The reasons for using a damp paper towel and a plastic bag is to ensure that the leaves (and therefore the mildew spores) are not jostled into the air, where they could very easily spread to nearby plants. Once the infected leaves are removed, growers should tie the bag tightly and dispose of it in an enclosed receptacle.

There are also many home remedies that growers can employ to treat an outbreak of powdery mildew on their cannabis plants should one occur. For instance, a mixture of 2 teaspoons of apple cider vinegar with 1 quart of water can be misted onto cannabis plants to kill active powdery mildew and also prevent it in the future. A mixture of teaspoon of baking soda and 1 quart of water will have similar results.

Oil sprays are also helpful in ridding a cannabis plant of powdery mildew. Specifically, growers can spray fish oil or neem oil onto their affected crops. These are often used by gardeners as natural remedies for fungi or other airborne garden pests.

One surprising method of fighting and treating powdery mildew is to spray a mixture made up of 60% water and 40% milk. That’s right, milk. Milk contains a protein that naturally forms an antiseptic when exposed to sunlight (or artificial light). Once the original infection has been taken care of, this mixture should be sprayed in bright light every 10 days to prevent further growth.

If nothing else is working to get rid of your pesky powdery mildew problem, it may be time to invest in a specialized product to help you treat the issue. Further natural, organic, and chemical remedies and products for treating powdery mildew on cannabis plants can be found on this marijuana growing website.

Nip it in the bud

Powdery mildew has the power to completely destroy your cannabis crops. While in this case, the best offense is a good defense, there is only so much that any grower can do to fight off an invisible spore flying through the air. If you do notice powdery mildew growing on your crops, it’s not the end of the world, just make sure you work hard to remove the infestation and prevent it from spreading any further. Remember, you can save your plants if you catch powdery mildew early enough!

Author: Daphne Eccleston