Question From: J. Kordziel - Mineville, New York, United States
Q: What causes and what can be done for white powder on cosmos leaves?
You have powdery mildew. A fungicide, such as ACTINOVATE will control it, but not erase the damage. A good emergency spray is 1 part milk to 9 parts water sprayed on the top and bottoms of the leaves every 4 to 5 days or right after it rains. Best And Happy Yardening, Nancy