A period of at least 6 hours at 100% humidity on the leaf surface is required for infection. Downy mildew symptoms vary considerably, plant to plant. Lesions appear first on the oldest leaves and then spread to the younger leaves.
Do not crowd plants. Avoid overhead watering to minimize leaf wetness. Spray a copper soap fungicide as a protectant. We recommend Soap-Shield Flowable Liquid Copper Fungicide.