Symptoms. Round or irregularly-shaped patches can appear very quickly on turf that is cut closely, such as for golf greens, or on turf that is very wet. The patches may be small, or up to 20 inches or more in diameter. At first the patches are purplish green in color, but they soon fade to light brown. If the weather is warm and humid, the fungus continues to invade new grass on the edges of the patch, so that there may be a dark purplish to grayish brown border surrounding the spots. This sometimes is called a 'smoke ring', and it is usually noticeable only in the early morning while the grass is still moist from dew. The ring consists of recently infected plants that have become covered with a web of fungal growth. The smoke ring is considered to be diagnostic of this disease. Symptoms for strains of this fungus that cause disease at times of the year other than summer and early autumn are generally light brown to yellow rings or patches.
On turf that is cut less closely, such as a lawn, the patches are light brown, and usually are round. There is no smoke ring. The affected grass usually lies flat to the ground, giving the patch a sunken appearance. The patches are usually about a foot across, but if the weather is wet, they may be enormous, up to 45 feet in diameter. In the center of the patch, the grass may recover because the crowns of the plants have not been killed or those plants may be unaffected. This pattern is sometimes called a 'frog-eye', and looks like a ring or donut.
Individual leaf blades may have spots on certain varieties that are high cut. Spots are watersoaked at first, then become tan in color, and have a dark border. Dark brown to black hard structures that are about 1/8" in length may be seen in the thatch layer or in the leaf axils. These are the structures the fungus uses to survive the winter or dry conditions.
Prevention. Dense stands of well-fertilized turf are generally most susceptible to this disease. Avoid excessive nitrogen fertilizer. Balance fertilizer applications with phosphorous and potash applications. Apply fertilizer only after a soil test indicates the levels needed. Keep thatch layer to less than 3/4".
Good drainage, both surface and subsurface, is necessary to keep canopy humidity to acceptable levels. Water early in the day to allow leaves to dry quickly. Remove dew from grass early in the morning by poling or dragging a hose or a burlap bag over the turf. Removal of hedges, shrubs, or trees may improve air circulation.
Resistance is not available to this disease. See current recommendations for chemical control measures.
By Pamela S. Mercure, IPM Program Assistant, University of Connecticut, 1998
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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