Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; firstname.lastname@example.org
Downy mildew of spinach has been found in the mid-Atlantic. This disease is not common in Maryland or Delaware, but I do see it occasionally. Symptoms begin with light spots on the upper surface of the leaf, followed by purple to grey fungal growth on the lower leaf surface (Figure 1).
Figure 1. Downy mildew sporulation on spinach leaves.
White rust (Albugo occidentalis) occurs more frequently in Maryland and Delaware. White rust symptoms begin with light green areas on the upper surface of the leaves. However in the case of white rust, the sporulation on the underside of the leaves is white, not grey (Figure 2). A third common spinach disease is anthracnose (Figure 3). Anthracnose is characterized by small tan lesions on leaves. Scout your spinach plantings and determine whether a disease is present. See the Commercial Vegetable Recommendation Guide for several effective fungicide options. Read the labels carefully because some fungicides applied at high temperatures may be phytotoxic, and many available and effective products, if used improperly, will result in resistance development. Alternate fungicide classes within a spray program, and follow resistance management guidelines on the label.