Downy Mildew
Downy mildew is a type of fungus that becomes active in the vineyard when shoots are about 10 inches long.
Role of Downy Mildew in the Vineyard
A fungus called Plasmopara viticola is responsible for this scourge. It thrives in humid conditions and remains dormant in the soil over winter. Downy weakens vines during winter when they are dormant, and can cause negative effects in a vineyard that can last for years. It is more apt to reoccur in vineyards that have had previous problems with it.
During early spring, rain splashes the dormant spores in the ground up to leaves on the vine. Downy mildew attacks grape clusters in late spring and early fall. It decreases grape yields.
Most Vitis vinifera varietals are prone to downy mildew. Varietals from the Pinot and Cabernet Families are particularly susceptible. Native American varietals and hybrids are more resistant. Strobilurin is a type of fungicide used to treat downy mildew.
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