Begin sprays when vines run, or earlier if symptoms are detected. Alternate chlorothalonil or mancozeb with Quadris every 7 days. This is especially important to delay the development of resistant strains of the pathogen to Quadris. Apply chlorothalonil or Quadris on alternate weeks when using these fungicides. Generally occurs from mid-July until the end of the season.
Excellent resistance is available in some varieties.
Use resistant varieties when possible. Observe fields for the presence of powdery mildew. When one lesion is found on the underside of 45 old leaves, alternate chlorothalonil with Flint or Quadris every 7 days. The registration of another fungicide with a different mode of action against powdery mildew is anticipated for the 2000 growing season. This fungicide will be recommended to be combined with chlorothalonil in this program.