Warm days and cool nights are happening now. These are perfect conditions for powdery mildew to thrive in the garden.
This common disease is easily recognized by the talcum-powder like appearance on new and old leaves, tender new shoots, some flowers, and fruits. It affects a huge range of plants – roses, crape myrtle, sycamore, oaks, begonia, chrysanthemum, dahlia, sunflower, and zinnia are some of the more common ornamentals afflicted by the disease. Apricot, nectarine, peach, plum, strawberry and grapes are susceptible to the disease along with many vegetable crops and lawns.
On some plants, the disease’s white, powdery appearance may simply be an unattractive nuisance, while on others it can cause severe injury. Leaves and shoots may be covered with it and become distorted, dwarfed, and discolored. On the new growth of live oaks, it can produce “witches’ brooms”; on other plant types, it may result in premature leaf drop.
Vegetables can display white, powdery spots that gradually spread over large areas of leaves and stems, though on artichokes, onions, peppers, and tomatoes it looks more like yellow patches on leaves rather than powdery growth. Diseased plants can have reduced yields, shortened production times, and fruit with little flavor.
This fungal disease prefers dry conditions, mild temperatures, in the range of 60° to 80°F, and shady locations the most favorable for disease development. It’s sensitive to extreme heat and sunlight, and some can be killed if the leaf temperature goes above 90°F.
Prevention is the best method of controlling this prolific disease.
- Selecting varieties of plants that aren’t susceptible to the disease
- Plant in a location with full sun and good air circulation
- Maintain a “clean” garden (pick up and dispose of any infected leaf material)
- Avoid using excess fertilizer
If infection is severe, avoid fertilization and overirrigation. Prune during the proper time of year to increase air circulation and sun exposure.