Symptoms. Round spots, 1" to 2" across, appear suddenly in hot, humid weather. The spots usually appear in clusters. They may grow very fast and are usually larger on lawn grasses than on golf greens. Patches often grow together and their spread may follow the direction of mower movement. Patches are dark at first, then fade to a tan to reddish-brown color.
When they are first infected, leaves are water-soaked, dark and slimy in the early morning . When they dry, they become reddish brown, then tan and shriveled. If the humidity is high, the patches may become covered with fluffy, white, fungal growth. When weather is less favorable, the leaves at the edges of the patches may have distinct white or straw-colored spots or bands on the blades. The edges of these spots or bands are the same color as the centers.
The spring species of Pythium causes a reddish color to the turf and infected plants are usually scattered throughout the turf rather than in patches.

Prevention.

• It is important to keep the plants from remining wet for excessive amounts of time.
• Provide good surface and subsurface drainage when establishing new sites.
• Water as deeply and as infrequently as possible.
• Avoid overwatering.
• Avoid watering late in the day, when the leaves will not be able to dry before night.
• Remove thatch if it is more than 3/4" deep.
• Do not overfertilize, especially with nitrogen, but use a balanced fertilizer.
• Do not mow wet grass.
• Prune trees and shrubs to increase air flow and light penetration.
• See current recommendations for chemcal control measures.

By Pamela S. Mercure, IPM Program Assistant, University of Connecticut, 1998.

References.

Smiley, R.W. 1983. Compendium of Turfgrass Diseases. APS Press, St Paul, MN.

Smith, J.D., N. Jackson, and A.R. Woolhouse. 1989. Fungal Diseases of Amenity Turfgrasses, Third Edition. E. & F.N. Spon, London.

Turgeon, A.J. 1996. Turfgrass Management, Fourth Edition. Prentice Hall, Upper Saddle River, New Jersey.

This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

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