Biology and Management of Downy Mildew of Lettuce

Downy mildew of lettuce is caused by the fungus-like organism Bremia lactucae. This pathogen is an obligate parasite, which means that it can grow and reproduce only on living plant tissue. Downy mildew is a major disease in lettuce production systems worldwide. Downy mildew on vegetable crops other than lettuce grown in Arizona is caused by other fungus-like organisms, but not by Bremia lactucae. Disease epidemics can be devastating when environmental conditions are favorable for disease development. In semiarid to arid climates like Arizona, disease intensity and crop loss are highly dependent on weather factors.

This article describes the factors affecting development of downy mildew of lettuce and provides disease management strategies.