Symptoms. This disease has two phases, the leaf spot phase and the crown and root rot, or melting-out, phase. Leaf spots occur during cool, humid weather in the spring and fall. Older leaves are more susceptible. Small, dark, round ,reddish-brown to purplish-black spots appear on the leaves. They may be surrounded by a yellow ring. The spots grow to an oval. The centers die, turning light brown to almost white. On a few species, these fungi can cause a net-like pattern of brown streaks and spots. Spots may occur on leaves, sheathes, and stems. In severe cases, the stem spots may completely encircle the stems, killing the plant above the spot. This can severely thin the stand.

Warm dry (or dry after wet) weather is favorable to the crown rots phase of this disease. On susceptible cultivars, the fungus may invade the roots and crowns, and cause a reddish-brown dry rot that later becomes black. The plants wilt, drop their leaves, and turn yellow to brown as they die.

Prevention.  

• Apply fertilizer sufficient to encourage moderate growth.
• Avoid over-fertilizing, especially in early spring and mid-summer.
• Avoid overuse of fungicides and weed-killers, as these may accentuate these diseases.
• Water early in the day, and as deeply and infrequently as possible.
• Mow grass as high as possible.
• Remove thatch in early spring if it is deeper than 3/4".
• Prune trees and shrubs to promote light penetration and air circulation.

Resistance is available to this disease. See current recommendations for chemical 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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