How do I prevent hop infestation?

Keep the vines well fed and watered and evenly spaced. Be sure to keep the area free of weeds. Avoid watering the plants late in the day, fungal and mildew growth needs moisture and darkness. Early watering allows the vines to dry off for the night. Powdery mildew will appear beneath the leaves - Trim off infested parts and dispose of in the trash, away from the vines (do not put in a compost pile).