By George Kuepper
NCAT Agriculture Specialist
March 2003
Downy mildew, caused by the fungal organism Pseudoperonospora cubensis, is most destructive to cucumber and cantaloupe, though all cucurbits are susceptible. Symptoms first appear as pale
green areas on the upper leaf surfaces. These change to yellow angular spots. A fine white-to grayish downy growth soon appears on the lower leaf surface. Infected leaves generally die but may remain erect while the edges of the leaf blades curl inward. Usually, the leaves near the center of a hill or row are infected first. The infected area spreads outward, causing defoliation, stunted growth, and poor fruit development. The entire plant may eventually be killed (1, 2).