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Problem: Grapes, Downy Mildew
Hosts: Grapes
Description: This
wet-weather fungus attacks both the leaves and fruit. Small yellow spots initially develop
on the upper surface of the leaf. If you flip the leaf over, you will find a fluffy white
growth on the surface. This should not be confused with powdery mildew that causes a dusty
white growth on the upper leaf surface.
Recommendations: If you have been on a regular spray program to control powdery mildew and black rot using Nova, Bayleton, or Rubigan, you may be vulnerable to downy mildew. The fungicide metalaxyl (mixed with copper or mancozeb) is very effective against downy mildew but cannot be used within 66 days of harvest. Some products that might be effective now include Abound, Captan and possibly Ziram.
References:
1. Horticulture '98, K-State Research and Extension
Horticulture Newsletter, No. 31, August 5, 1998
Last Update: 03/28/2003
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