Medical cannabis seeds are susceptible to powdery mildew, a general term for a variety of harmful plant fungi, once they start to grow leaves. If left unchecked, the mildew can damage and eventually kill an otherwise healthy marijuana cannabis plant. The fungus grows over the leaves, killing the plant tissue lying underneath the growth, and can spread quickly to nearby plants.
Powdery mildew is easy to miss at first because the fungus looks like a light coating of dust or powder on the marijuana cannabis leaves. Rubbing the plant’s leaves removes some of the mildew, making it seem as if the “dust” can be simply wiped off. However, the mildew will appear to return in full force and continue to grow, taking on a distinct white circular pattern while spreading over the marijuana cannabis plant’s leaves and buds. The leaves wilt and drop off, and growth slows or might stop altogether. The harvest is commonly lost without management or treatment. The fungus takes nutrients from the cannabis plant during the infection, so the overall state of the plant declines as the fungus spreads.
Prime conditions for the growth and spreading of powdery mildew include temperatures between 60 and 70 degrees and a high humidity level – two common growing conditions of medical cannabis seeds – and an acidic environment. Once one cannabis plant has been infected by the tiny fungi spores traveling through the air, it can easily pass the infection to the other plants by releasing spores from the white patches on the leaves, especially if the plants are close together. The spores are tiny black dots within the circular mildew patches. Dead leaves from an infected cannabis plant that fall on the ground contain these spores, and the spores can pass to other plants.
Powdery mildew can be managed by changing the growing environment of the medical cannabis seeds, including raising the temperature over 70 degrees and lowering the level of humidity. Leaves that fall from an infected plant should be picked up immediately to stop the spread of the fungus to other plants, and the grower should not touch a healthy plant after picking up infected leaves without cleaning his hands first. Moving an infected plant away from healthy plants, if possible, helps stop the spreading of the spores throughout the rest of the crop. Some commercial bio-fungicides and less harmful fungi killers can be safely used on medical cannabis plants, such as cinnamon and copper-based plant treatment products. Neem oil, from the nut of the Neem tree, and sulfur suffocate mildew without the use of harsh chemicals. Common baking soda can be diluted with water or milk and periodically applied to the cannabis plant leaves to destroy mildew, but because cannabis plants can’t take large amounts of sodium, any left behind bits of baking soda must be washed off before applying more. Harsh chemical fungicides should not be used on medical marijuana cannabis plants. Chemicals not approved for crops for human consumption can kill the cannabis plant and will make the harvest unfit for use by patients.