The white powdery mildew sometimes seen on phlox, helianthus, lilacs, dogwoods, and the like at this time of year is rather unsightly. This fungus spreads, so be sure to avoid working with these plants during wet weather. Do not handle the leaves at all if you can help it!
We have had success with soil amending to correct mildew, as it is a sign of a lack of potassium and micronutrients. Preventative sprays are available in an organic program, and are best applied starting back in June. Once the white fungus appears, it is on the leaves for good that season. Dividing the plants to promote better air circulation will help, as will careful siting away from areas where there is never a breeze stirring, such as against a stone wall or foundation.
Let us test your soil and develop a program to combat the powdery mildew syndrome this fall. Contact Kimberly for details, firstname.lastname@example.org.