This fall the ISU Plant Disease Clinic received several inquiries regarding Kentucky bluegrass lawns with large areas with a white talcum powder-like film. One client described symptoms looking like spray paint. Someone else stated that the white powder was getting on his or her shoes. The white substance observed on the blades is composed of millions of spores and mycelium (thread-like strands) of the powdery mildew fungus.
Powdery mildew infections are more common than normal this season. Many fall days have been overcast with temperatures hovering in the 60s, perfect for the development of powdery mildew. The disease is often particularly severe under these conditions when the lawn is heavily fertilized with nitrogen.
The best strategy for controlling powdery mildew is to plant shade-tolerant cultivars in shady areas. For cultural control, avoid excessive nitrogen fertilization and selectively prune trees or shrubs, if practical, to increase air circulation and sun penetration. Fungicide applications are rarely necessary.
This article originally appeared in the December 7, 2001 issue, p. 125.