![]() ![]() We comply with the Federal Trade Commission 1998 Children’s Online Privacy Protection Act (COPPA). The 4-H Name and Emblem have special protections from Congress, protected by code 18 USC 707. Reference to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned. This information is for educational purposes only. Quentin Tyler, Director, MSU Extension, East Lansing, MI 48824. Issued in furtherance of MSU Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Michigan State University Extension programs and materials are open to all without regard to race, color, national origin, gender, gender identity, religion, age, height, weight, disability, political beliefs, sexual orientation, marital status, family status or veteran status. MSU is an affirmative-action, equal-opportunity employer, committed to achieving excellence through a diverse workforce and inclusive culture that encourages all people to reach their full potential. Commercial biological treatments for fighting downy mildew are. Use the 10-10-10 rule to decide when to start scouting for downy mildew: at least 10 cm (4 in.) of shoot growth, 10 mm (0.4 in.) rainfall and temperatures of 10 degrees Celsius (50 F) during a 24-hour period. The disease also affects the fruits and other plant parts. The disease can spread rapidly under warm conditions with frequent rain or dew. Lesions appear 5 to 17 days after infection. In spring, spores are carried by rain splash to new leaves, where they require a film of water for infection. ![]() The pathogen overwinters in infected leaves on the ground. Although berries become resistant to infection within 3 weeks after bloom, the rachis remains susceptible for several weeks longer. Infected berries turn a mottled dull green or reddish purple and readily fall from the cluster. Infected flower clusters dry up or become covered with white spores under humid conditions. Severely infected leaves drop prematurely, which can reduce winter hardiness of the vine. ![]() The lesions eventually turn brown as the infected tissue dies. Under humid conditions, white, downy spore masses can be seen on the lower leaf surface. Initial leaf symptoms are light green to yellow spots, called “oil spots” because they appear greasy. Downy mildew is a widespread, serious disease of grapevines. ![]()
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