As summer starts to fade and autumn approaches, there is much variability in the weather. Some days are rainy and humid, others are hot and dry, and the nights are noticeably cooler—ideal conditions to see symptoms of powdery mildew on plants, trees, fruits or vegetables. But what exactly is powdery mildew?

Powdery mildew is a common name for diseases caused by fungi within the order Erysiphales, all united by that tell-tale symptom of a fuzzy, whitish mat or spots on its host. These obligate parasites differ in their host plants, but they thrive and proliferate in the fluctuating conditions felt around this time of the year. Host symptoms can depend on several factors, such as the host’s species, age, and part infected, yet an infection rarely causes death. The range of signs includes: necrotic spots; color change or leaf curling; dwarfed or distorted fruits and flowers; or there may be no visible symptoms.

This set of IDaids explores powdery mildew disease, including some of the commodities it affects and the organisms that cause it.