e welcome end of a four-year drought brought one unexpected hardship to some California wine grape vineyards: downy mildew. Veteran extension viticulturists said the pathogen is a rarity in the Golden State and blamed its emergence on uncommon rates of humidity due to alternating hot and cool, damp and dry spring weather. While powdery mildew is routinely encountered and treated in the West, downy mildew is far more common in eastern and Midwestern vineyards, where the growing season is dominated by higher heat and humidity.

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