The initial symptoms of powdery mildew show as small white dots on the upper surfaces of the leaf. The fungus leaves a characteristic powdery appearance on the leaf surface and may look similar to dust or spider mites.
As it matures, the affected areas may develop a greyish color, and the leaves will begin to curl and become distorted when powdery mildew on cannabis gets serious.
Above 50% humidity and poor air movement increases the risk of powdery mildew developing.
Prevention – Environmental Conditions
Powdery mildew is often a result of poor environmental management in situations that create conditions suited for powdery mildew infection. During the flowering stage, humidity needs to remain in the 40-50% zone with air movement throughout the growing area.
Temperature fluctuation is also important. Temperature change causes condensation, which facilitates the growth of powdery mildew on cannabis.
Treatment
Powdery mildew treatment is first done through application of organic treatments in the early stages of infection. Milk spray made by mixing 1 part of milk to 10 parts water creates an alkaline environment on the leaf surface that will inhibit fungal species from infecting cannabis plants. Baking soda treatments work well also, it is diluted with one teaspoon of bicarbonate to one quart of water and will eliminate mild powdery mildew, and is also a recommended treatment of choice.
For moderate to severe infections, you may want to purchase a commercially available fungicide product for powdery mildew on weed. Typically, these commercial products provide a more aggressive treatment. Apply treatments when the lights are out (the lights are off so that you don’t burn the leaves) and thoroughly cover all areas that show infection.
Organic Management Options
Neem oil is a great tool to use against powdery mildew, and is safe to consume. You may want to use neem oil as a preventative treatment on a weekly basis, or as an effective treatment every few days when dealing with an active infection. Potassium bicarbonate solution is safe and effective for treating powdery mildew, and strips the leaves virus from active infection by altering the leaf’s surface pH making it hostile to the fungal spores.
Essential oils, (i.e. rosemary, thyme and tea tree oil) have shown antifungal properties and are effective against powdery mildew also. Essential oils can be mixed with water at an approximate 1 part oil to ten parts water plus a few drops of soap (dish soap preferably). You can blend together your mix and use it as a spray to treat powdery mildew on marijuana without exposure to harsh chemicals.
Prevention – Growing Practices
Ensure that you remove lower branches that touch the soil and keep your growing area clean. Sanitize your tools in between each plant.
Effective treatment of powdery mildew requires vigilance in managing your plant’s environmental conditions along with environmental best practices. Growers who are able to have success in preventing the development of powdery mildew on cannabis plants and manage their environmental conditions will also rarely find themselves overwhelmed due to having to deal with severe infections. Without doubt, effective environmental controls is the best long-term approach to managing this common challenging problem for cannabis cultivators.