Wednesday, March 19, 2008

What is Downy Mildew?

Downy mildew is a wet weather fungus that attacks leaves and fruits. Although its name sounds similar to powdery mildew, downy mildew is very different. Downy mildew favors cool, moist conditions. Downy Mildew begins as irregular yellow patches on leaves, that later turn tan to brown. It will eventually spread to the leaf, stem flower or fruit. If conditions are favorable, a dirty white, fluffy growth will appear on the underside of the leaves. Seedlings will often wilt and collapse, mimicking nutritional deficiencies. There are several ways to combat downy mildew. Smart growing techniques are key.
  • Promote good air circulation and leaf drying; use wide spacing between plants.
  • Select sites with good drainage and air movement.
  • Avoid overhead irrigation.
  • Water early in the day to allow leaves to dry thoroughly.
  • In the greenhouse, the use of blue polyethylene sheets to filter the light has been shown to decrease spore production by the fungus. This did not increase the yield.
  • Resistant cultivars are available.
  • Seek a variety of control products. Switching treatment plans from time to time has proven to be effective, in most cases.

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