Powdery mildews are characterized by spots or patches of white to grayish, talcum-powderlike growth. Tiny, pinhead-sized, spherical fruiting structures that are first white, later yellow-brown and finally black, may be present singly or in a group. These are the cleistothecia or overwintering bodies of the fungus. The disease is most commonly observed on the upper sides of the leaves. It also affects the bottom sides of leaves, young stems, buds, flowers and young fruit. Infected leaves may become distorted, turn yellow with small patches of green, and fall prematurely. Infected buds may fail to open.
- Level of Concern
- Low / None
- What months
- Jul–Oct
- Treatment / Useful Links
Best avoided by using drip irrigation and eliminating water spray on leaves. Watered-down milk can be used as a preventive treatment, but hasn't been shown to be effective once mildew has set in. Affected leaves can be removed. Crop should be washed before eating, but is fine for consumption.
Apply preventative milk treatment at first sign of monsoons (early July). Use a mixture of 1 part milk, 2 parts water to spray all foliage as a preventative measure. If any mildew is noted, prune off diseased plant material, being sure to throw it away (not in compost) and clean tools and gloves throughly so as not to spread to other plants in the garden. Use a separate pruning tool and pair of gloves only for PM if possible. Other preventative measures include: avoid overhead watering of plants that are susceptible, avoid late summer applications of nitrogen rich fertilizer. Helpful link: http://www.ext.colostate.edu/pubs/garden/02902.html