As summer winds down and nights begin to cool the plants in your garden face a new threat, says Master Gardener, Bridget Tisthammer, in an August 16 report on the Coloradoan. Warm, humid days and cool nights provide the ideal breeding ground for powdery mildew that can infect veggies and flowers in your garden.
Powdery mildew looks like someone sprinkled the foliage of your plants with a grayish-white powder. In the initial stages, this fungal infection is merely cosmetic, but it soon causes the foliage to wilt or distort, turn yellow and drop from the plant.
In Maine, powdery mildew typically affects squash, cucumbers, and other members of the cucurbit family.
Prevention, of course, it the best remedy. Growing resistant varieties and leaving plenty of space between plants when planting helps in preventing powdery mildew. Avoiding overhead watering and watering plants early in the morning so the foliage dies in the summer sun also helps prevent powdery mildew.
Treating powdery mildew when it first appears with neem oil, or other horticultural oils, may eradicate powdery mildew, but once the disease has spread, there is little you can do says the University of California Extension Services. Other fungicides, such as wettable sulfur applied before your plants show sign of powdery mildew may be effective in preventing the disease.