Powdery mildew

Jody Fetzer, Maryland National Capital Park
and Planning Commission

The powdery mildew fungus is easily spread through the air and, unlike many other foliar diseases, does not require wet conditions for infection to occur. Powdery mildews thrive when the temperature is cool and relative humidity is high. Severely infected leaves become brittle and wither and die.

Many types of powdery mildew fungi have extremely narrow host ranges. They have absolute specificity in what they can attack.

One aspect that lends these pathogens to be extremely virulent is the fact that the spores are very easily spread by wind. The spores also can overwinter and cause infections the following spring.