Mix 1 tablespoon potassium bicarbonate and 1/2 teaspoon liquid soap in 1 gallon of water. Spray cannabis leaves every 7 days. This stops powdery mildew. For active spots, mix 1 cup of 3% hydrogen peroxide in 1 gallon of water. Spray once. Repeat after 3 days.
how to treat powdery mildew on cannabis leaves
Why These Sprays Work
Powdery mildew is a fungus. It grows on leaf surfaces. Potassium bicarbonate changes the pH on the leaf. That kills the fungus. Hydrogen peroxide kills spores on contact. It breaks down into water and oxygen.
Will Washing Buds Remove Powdery Mildew? No, and Here's Why
Recipes
Potassium Bicarbonate Spray
- 1 tablespoon potassium bicarbonate
- 1/2 teaspoon liquid soap (castile or dish soap without bleach)
- 1 gallon water
Mix. Spray leaves top and bottom. Use within 1 day.
Hydrogen Peroxide Spray
- 1 cup 3% hydrogen peroxide
- 1 gallon water
Mix. Spray leaves. Do not spray buds.
best organic fungicide for weed powdery mildew
Milk Spray
- 1 part milk
- 9 parts water
Mix. Spray leaves. Milk can leave a smell. Use before flower.
Baking Soda Spray
- 1 teaspoon baking soda
- 1 quart water
- 2 drops liquid soap
Mix. Spray leaves. Baking soda adds sodium to soil. Do not use in flower.
How to Apply
- Spray in early morning or evening.
- Spray the top and bottom of leaves.
- Keep lights off until leaves dry.
- Repeat every 7 days for potassium bicarbonate. Repeat hydrogen peroxide after 3 days.
- Stop spraying 3 weeks before harvest.
Limits
Homemade sprays work on early infections. They do not cure severe infections. Remove infected leaves. Increase air flow. Keep humidity below 50%. If mildew returns, use a commercial fungicide. Check your state rules for cannabis products.
Powdery mildew on cannabis is common indoors. It spreads when humidity is 60% to 70% and temperature is 68°F to 77°F. A spray with potassium bicarbonate is exempt from EPA registration. Milk sprays showed 40% control in some tests. Baking soda can burn leaves. Test on one leaf first.