Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
White rust can be a problem on cole crops, such as collards, during the spring and fall. The disease is most severe during cool weather where dew forms at night and the days are warm but not hot. Symptoms of this disease are small (about 1/8 inch diameter) white or cream-colored, blister-like lesions on the underside of leaves, or on the flower stalks. Initially a thin layer of leaf tissue covers the lesion, but this layer eventually ruptures and the spores are released. On the upper leaf surface chlorotic spots develop.
Control measures include good sanitation practices, such as plowing the infected crop residue into the soil. Closely related weed species are also hosts and should be controlled to reduce inoculum. Seed treatment prior to planting (either with a fungicide or hot water seed treatment) should be practiced to reduce inoculum from infested seed. A few resistant cultivars are available and should be used if possible.
During the season disease can develop despite the best efforts of growers. When foliage is infected, fungicides such as strobilurins can be helpful in reducing losses.
White rust (Albugo candida) on mustard (Brassica spp.).