At last! With this warmer weather and brief dry periods, many of you are out enjoying your gardens. What a thrilling and indulgent time of year in the PNW!

The recent weather pattern we’ve been experiencing has made conditions favorable for the spread of powdery mildew, and we want to bring this to your attention because it’s best to respond to powdery mildew early. It’s not often lethal to plants, but can cause damage or leaf curl, and is likely to spread if not controlled. Maybe some of you are already seeing it settle in your garden?

Powdery mildew appears as white spots of a baby powder-like coating on pea plants.

Powdery mildew arrived on these pea plants mid-June this year in a Seattle garden, though it can affect a variety of plants in our gardens, from squashes to dahlias, as well as apple trees and native species among others.

Certain plants and locations in your yard might be more susceptible. Powdery mildew is a fungus that prefers dry plants and warm (60-80°F), humid conditions. Our temperatures have been delightfully warmer, and the pattern of rain has brought consistently high humidity. No, it hasn’t been particularly dry recently, but plants close to buildings or under the protection of trees might remain drier. Plants under the eaves of buildings will also receive extra heat emitted from the heat sink of the building and may be particularly susceptible. Plants with dense growth habits are also more susceptible because they trap in moist air and lack good airflow.

Plants that have been fed high nitrogen fertilizers are also more susceptible. Large quantities of nitrogen encourage fast plant growth which leads to thin-walled, succulent plant tissue. These conditions make for favorable host sites, since powdery mildew is a fungus that infects the surface cells in plants.

Getting rid of and preventing it
There are steps we can take to prevent, and if necessary, remove powdery mildew. Using well-balanced fertilizers and amendments helps feed sturdier plants. Building the microbial life in the soil, such as with our brewed probiotic FertileTea, assists plants’ natural immune systems. Pruning plants that have dense growth allows sufficient airflow. But we cannot control the weather. If powdery mildew settles in your yard, it’s best to control immediately before causing damage to the plant or spreading to other plants. Removing infected areas where possible can help mitigate the presence of powdery mildew during fluctuating weather like we are currently experiencing.

Powdery mildew settles on ajuga in a client’s property in Tacoma this June.

At Earthdance Organics, we use a naturally occurring bacteria as a control for powdery mildew. This bacteria, packaged as Actinovate, works in a symbiotic relationship with the plant, attacking only the fungus, not harming plants, animals, or insects. We offer this as an additional service for Lawn Care Program clients. Please call if you’re seeing powdery mildew and we will schedule you for service ASAP, or if you have questions about how you can control this on your own. Send us an email to [email protected] or call us at (253) 927-2523.