The best defense against attack by pests and diseases is to grow the healthiest, hardiest hops possible. Selection of disease-resistant cultivars is the first step. Next, select a sunny site with good drainage. Despite our best efforts, hops may be attacked by diseases and pests. Pests generally include aphids and mites.
Downy mildew is the most common disease.
Avoid the hot, moist conditions that favor spore germination. This is why it is better not to use sprinklers to water the plants. If you must sprinkle, do so in the morning so the leaves and shoots can dry. Powdery mildew is another fungus. Systemic or spray fungicides for downy mildew and sulfur-based fungicides for powdery mildew can be used as a last resort.