As spores are produced, the colony takes on a white, powdery appearance.
Infection occurs following spring rains or sprinkler irrigations.
During years when weather is conducive for rapid pathogen reproduction, inoculum concentrations remain high throughout the growing season. Begin treatment at budbreak to 2-inch shoot growth. Reapply if sulfur is washed off by rain or irrigation. Treatments may be discontinued for wine and raisin grapes when fruit reaches 12 Brix but should be continued to harvest for table grapes. During cool springs when growth is slow, an additional wettable sulfur treatment is advisable 10 days later.