ARAgriculture Home Powdery Mildew Powdery mildew, caused by the fungus Erysiphe graminis, generally has not been a serious problem in Arkansas during the past few years except on a few varieties. Symptoms appear on leaves and leaf sheaths as tufts of off-white cottony fungal growth that can be rubbed off. The fungus produces asexual spores on the fungal growth and sexual spores in black fruiting bodies that may develop later. The disease can be found in many fields during stem elongation stage, but on most varieties it tends to disappear as the season progresses. Caldwell and Keiser are two varieties that are exceptions to this generalization, and powdery mildew has occurred on flag leaves and heads of these varieties in the past.
Most varieties are resistant enough under Arkansas conditions that no other measures are required.
However, there are races of the powdery mildew fungus just as there are races of the rust fungi. New races may develop to cause disease on varieties that are now resistant. Powdery mildew can be controlled early in the season by Baytan seed treatment, and Bayleton or Tilt foliar fungicides are very effective in the spring. However, no special seed treatment is advised unless a susceptible variety is being planted in an area with a history of powdery mildew. No foliar fungicides are warranted unless disease is still progressing up the plant at boot stage.