Late summer is prime powdery mildew season. Probably one of the simplest and easiest answers is to use horticulture oil or horticulture soap. You should be able to get it at a good garden center. Be sure to use a low concentration of 1%.

When using chemicals, always make sure it is labeled for whatever you want to treat. So the label should say it treats powdery mildew. And always follow the application directions.

You can also try potassium bicarbonate (not sodium bicarbonate which is baking soda, but potassium bicarbonate). Milstop® and Armicarb® are two brand names with potassium bicarbonate as the generic ingredient.

For tips on a variety of gardening topics, see our Plant Information Guides.

- Courtesy of NYBG Plant Information Service