Winter wheat leaf infected with powdery mildew in Alburgh, Vermont.
The cool wet weather throughout the spring has created the ideal growing conditions for a plethora of fungal pathogens. Several leaf diseases have been observed in our grain trials this season. One of the more easily identifiable ones is powdery mildew.
Powdery mildew is a common disease of grain crops and can be observed periodically on virtually any crop. Different fungi cause powdery mildew in different crops but all of the powdery mildew fungi are closely related. In grain crops, the causal fungi are mainly in the genus Erysiphe.
Powdery mildew first appears on the surface of the lower leaves as white powdery patches. If the conditions remain ideal for powdery mildew development, these patches will get larger, run together, and eventually cover large portions of the leaf. The white, powdery growth turns a dark yellow-gray with age. Many dark specks resembling grains of pepper (powdery mildew fruiting bodies) form in these patches later in the summer. Yellow, necrotic lesions will appear on the lower leaf surface directly beneath the patchy areas of the mildew. Under the right conditions, the powdery mildew will move from the lower leaves to the upper leaves and occasionally will spread to the grain head.
Severe infection of powdery mildew can reduce yields by disrupting a host plant’s photosynthesis, respiration, and transpiration. Plants lose vigor and as a result, there is a reduction in grain fill.