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 forms a structure called a sporangium. The sporangium matures and germinates and produces another type of spore (zoospore). Sporangia are spread by wind and splashing rain and germinate in the presence of free water. 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. Contact your local Extension office for current fungicide recommendations. See Downy Mildew of Grapes for more information.

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