Joe Pye Weed diseased, powdery mildew?

Asked August 10, 2020, 9:54 AM EDT

I think my Joe Pye Weed has powdery mildew and has had for a couple of years. The leaves are whitish and leaves are dropping off from the bottom up. I cut the plant back and remove debris every year. How do I treat?

Anoka County Minnesota

1 Response

Cultural practices are really the best approach to powdery mildew. The fungi that cause it lives in the soil, so the very best thing to do it mulch well around the plants in the spring. This will prevent soil containing the fungi from splashing onto the plant during rain or watering. Remove affected leaves and plants. You may want to consider relocating the plants to another part of your garden, removing as much as the soil from the roots as you can.

There are fungicides that will treat powdery mildew, but you will be using them again and again each year without the cultural methods. Low impact fungicides are recommended, if you decide to go that route, like sulfur, potassium bicarbonate and horticultural oils. Here is an article on powdery mildew from the U of MN: https://extension.umn.edu/plant-diseases/powdery-mildew-flower-garden