Problem: Downy Mildew (Onion Family (including garlic))
This plant disease is caused by a fungus (Peronospora destructor) that attacks onions and shallots primarily, although garlic, leeks, and chives are also susceptible. The occurrence of downy mildew may be sporadic-appearing 1 year and disappearing the next-or it may continue for several consecutive years. It is most prevalent during cool, moist nights and warm, cloudy days. Most infections occur when the temperature is between 50° and 65°F. Downy mildew is especially troublesome during periods of heavy dew or high humidity, and many plants are killed at these times. If dry weather resumes before the plant dies, however, new growth may emerge. The spores are spread from plant to plant by the wind and die rapidly when exposed to the sun and low humidity.
Water by using drip irrigation. Clean up and destroy plant debris after harvest. Apply a fungicide labeled for this disease, following label instructions.