POWDERY MILDEW

Learn how to identify, control and prevent this common fungal disease.

- Marisa Reyes

Don't you hate it when lush peonies, zinnias or garden phlox (shown above) develop a gray cast to their foliage and start dropping leaves? You're not alone! Powdery mildew is one of the most common and frustrating fungal diseases gardeners face. It affects more than 10,000 plant species, including many of your favorite annuals, perennials, ornamental grasses and even fruits and vegetables. The good news? With the right knowledge and a few simple strategies, you can manage this nuisance.

WHAT IS POWDERY MILDEW?

While there are many species of powdery mildew fungi, they all create a similar white or gray coating on leaves, stems, buds, flowers and fruit. Each species targets plants in one family or genus and cannot survive without that host: The fungus that causes powdery mildew on linden trees won't affect lilacs.

Though rarely fatal, it can weaken plants over time, reduce their vigor, diminish flowering and impact fruit or vegetable yields.

HOW TO IDENTIFY IT

Powdery mildew presents itself in various ways, as you can see in the collection of photos below right. It often shows up first on the upper side of the leaf but in time will cover the entire plant. The leaves can also take on a distorted appearance or develop purple or red discoloration. In severe cases, the foliage turns yellow, twists or drops prematurely, buds fail to open and fruits develop stunted growth.