At the end of the growing season remove and destroy diseased annuals and prune out the diseased portions of perennials. Fungicides Chemical control of powdery mildew is generally not necessary when the disease occurs late in the season. By that time the leaves have already served their usefulness for that growing season and and will soon be senescing. Late season infections cause little permanent damage, even where the plant appears severely affected. When the disease occurs early in the season or when highly susceptible plants are infected, chemical sprays may be warranted.
Fungicides are most effective when applied immediately at the first signs of infection.
Fungicides effective against powdery mildew may contain ingredients such as benomyl, myclobutanil, fenarimol, triforine, thiophanate-methyl, or triadimefon. Read the chemical label to be sure the fungicide is cleared for use on the plant in question. The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication. Educational programs of the Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability, or national origin.