A water-soaked lesion can often appear at the base of the stem. Control can be achieved by using sterile potting media, clean pots, and fungicide-treated seed. Affected transplants should be rogued out and discarded. Control in the field can be achieved by using a two-year rotation with nonsusceptible plants, such as corn, to prevent the buildup of pathogenic organisms. Downy mildew, Peronospora spinaciae.
Diseased plants show yellow leaf spots which have a purplish fuzzy growth on their undersides.
These spots may quickly grow together, killing the infected leaf or the entire plant. The fungus which causes this disease is soil- and seedborne. It is favored by wet cool weather. Downy mildew is not usually important on spinach in Connecticut. If the disease becomes a problem, do not plant winter spinach, which may carry over downy mildew from one growing season to the next.