Do I need to rid the soil of powdery mildew fungus before planting something new?
I have transplanted flocks which had powdery mildew in its first garden to the second garden. In their second garden powdery mildew returned the following summer. I want to plan something different there next year. Do I need to do something to the soil to rid it of the powdery mildew fungus?
No, there is no need to treat your soil for the phlox powdery mildew. There are a variety of fungi that cause powdery mildew. They are specific to different types of plants. So, the fungi that cause powdery mildew on squash will not cause powdery mildew on phlox. If you are planting different types of plants in that area, then those fungi won’t infect the new plants. For more information about managing powdery mildew on phlox, see this fact sheet from University of Iowa State University Extension. Even if you were going to keep phlox in that area, we wouldn’t recommend soil application of a fungicide. Planting resistant varieties, increasing plant spacing, keeping foliage dry when possible are all things that can help.