DISEASES OF SMALL GRAINS - POWDERY MILDEW

Powdery mildew is a common disease of grain crops and, in fact, is a disease that one can observe from time to time on virtually any crop. Different fungi cause powdery mildew on different crops, but all of the powdery mildew fungi are closely related. In grain crops, the causal fungi fall primarily in the genus Erysiphe. Symptoms of powdery mildews are very distinctive and easy to identify. Watch for plants that look as though someone has sprinkled powdered sugar or talcum powder on the leaves.

Control of powdery mildew is very difficult. Resistant small grain varieties are available, but the pathogen population is very plastic, and changes in this population can lead to failure of resistant varieties after a short period of time. Modification of the environment can also be used to control powdery mildews, but can be difficult to achieve. Powdery mildews tend to be most severe when humidity is high (approaching 100%). A reduction in plant stand can help reduce humidity, but may not be economically feasible. Any practice that helps to reduce soil moisture (and thus humidity) may lead to a reduction in powdery mildew severity. Cultural practices such as crop rotation, and removal or deep plowing of infected plant residue are of limited value, because spores of powdery mildew fungi are easily transported in the air over long distances.