Are the leaves of some of your favorite plants covered with a strange powder that makes them look like they were dusted with flour? You have powdery mildew. A number of plants are susceptible to powdery mildew, such as phlox, lupine, hazel, birch, maple, roses, lilacs, monarda, grapes, gooseberries, squash and cucumbers. Over the past couple of years here, maples have been particularly affected. Squash and cucumber plants almost always have it in the early fall when the temperatures cool and the humidity rises.
