How Do You Control Powdery Mildew?


Quick Answer

Colorado State University Extension says to control powdery mildew, avoid over watering plants and applying excessive amounts of fertilizer. Organic Gardening advises gardeners to expose as much of the leaf's surface as possible to direct sunlight. Remove affected plant parts, and dispose of them in a tightly sealed bag.

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University of California, Integrated Pest Management Program, explains that fungicides containing sulfur, neem oil, triforine or potassium bicarbonate can be applied to some plants at the first signs of infection. These solutions only work on contact, so the plant must be re-sprayed as new growth emerges. Mildew-tolerant or mildew-resistant plants are less susceptible to powdery mildew.

Powdery mildew thrives in low, shady locations with high relative humidity. Spores create white or grey patches on the surface of plants. This is generally not harmful to the plant, although it affects the plant's appearance and can impact the flavor and yield of fruits and vegetables. The fungus occurs most commonly on the upper side of leaves, though it can be found on the bottom, and on the plant's stems, buds, flowers and fruit. Leaves containing powdery mildew turn completely yellow and die. This may expose the fruit of the plant to sunburn.

Powdery mildew spores are transported by the wind, and they do not require water to grow. The fungus can exist through the winter through the production of special resting spores.

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