Powdery Mildew

Causal Agent(s): (fungi ‑ Sphaerotheca fuliginea, Erysiphe cichoracearum)

The first symptom is a white to gray dusty material on the upper leaf surface [wmd17.jpg].  The fungus quickly spreads to completely cover the leaf surface.  Once the leaf is covered, it dies and has a crisp texture.  This disease is favored by high humidity, but not free water on leaves.   The fungus is best controlled with fungicide applications when symptoms are first observed.   It tends to occur on older leaves and later in the growing season,  so control is not usually warranted.  Two systemic fungicides, Benlate (benomyl) and Bayleton (triadimefon),  are no longer effective because of pathogen resistance.