alternatives to pesticides - plant disease - Powdery mildew
Powdery mildew is a white or grayish powdery coating on the surfaces of leaves, stems and buds. It germinates on dry leaves in high humidity and is commonly found on fruit trees, roses and big shade trees. Rain inhibits it and warm, damp nights encourage it. It can cause stunting and distortion of leaves, buds and growing tips, a general decline in plant growth, yellowing of leaves and premature leaf fall.
Prune and thin out excess branches to increase air circulation. Plant resistant varieties, and put them in sunny locations.
Least-toxic chemical control
Spray with a mixture of 1 gallon water, 3 teaspoons baking soda, 2 1/2 tablespoons horticultural oil and 1/2 teaspoon insecticidal soap. Spray this on an unobtrusive area of your plant first, and watch for signs of adverse effects before spraying your entire plant.
- Horticultural oils are also called summer oils; these are more highly refined than dormant oils, making them appropriate for use on leaves during the growing season. Consult a nursery to locate a suitable product and follow all precautions. Don’t use horticultural oils when plants are flowering.
- Insecticidal soaps highly refined liquid soaps (technically the potassium salt of fatty acids), sometimes combined with citrus oil. Soaps are normally mixed with water and sprayed onto leaves to control spider mites, aphids, scale insects, whiteflies and other soft-bodied insects. They are contact insecticides, meaning you must wet the pest for them to be effective. As always, follow package directions and cautions when using these products