Your grapes may have downy mildew, which is a problem that can return every year. Unless the treatment you are using is for that specific problem, it may not do anything. Contact your local Extension office and ask about their plant diagnostic services. Once you diagnose the problem, you can get the specific control agents. Downy mildew is caused by the fungus Plasmopara viticola. The fungus overwinters in infected leaves on the ground and possibly in diseased shoots. The overwintering spore (oospore) germinates in the spring and produces a different type of spore (sporangium). These sporangia are spread by wind and splashing rain. Control: *Any practice that speeds the drying time of leaves and fruit will reduce the potential for infection. *Sanitation is important. Remove dead leaves and berries from vines and the ground after leaf drop. It may be beneficial to cultivate the vineyard before bud break to cover old berries and other debris with soil. Cultivation also prevents overwintering spores from reaching developing vines in the spring. * Grape varieties vary greatly in their susceptibility to downy mildew. *A good fungicide spray program is extremely important. Downy mildew can be effectively controlled by properly timed and effective fungicides.

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