Answer: What you describe sounds like powdery mildew, a fungal disease that attacks plants when nights are cold and daytime weather is warm. Phlox is known for its susceptibility to powdery mildew. Here are a few that are bred to be resistant to powdery mildew: 'David,' 'Eva Cullum,' 'Bright Eyes,' and 'Franz Schubert.' Don't crowd phlox as good air circulation helps prevent mildew. Also, clean up all plant material and discard it at the end of the season, and rotate where you plant species every year to help prevent build-up over time. Good luck!
Q&A Library Searching Tips