March 3, 2010 Issue Number XX

What Are The Brown Spots In My Centipede Lawn?

Question: Having read your article on dethatching a centipede lawn, I would like to know if you can tell me what the brown spots are that I began experiencing two years ago in my centipede lawn. Those brown spots have grown tremendously. Is this dieback as described in the article?

Answer: Probably the problem is brown patch or maybe dollar spot. Both are common lawn diseases.

Brown patch (or large patch) disease is caused by fungi, and most cool- and warm-season grasses are susceptible to brown patch. In fact, it is the most common and important patch disease of tall fescue in the Southeast.

Centipede is a warm-season grass, and most often brown patch appears in the spring as the turfgrass emerges from dormancy or in the fall as it goes into dormancy. Infections sometimes occur in midwinter.

Individual diseased patches may be several feet in diameter. Under drier conditions, the affected areas may be smaller and appear sunken because diseased leaves have collapsed. However, grass in the center of such patches may be unaffected or may recover more rapidly than grass at the margins. When this happens, a ring or doughnut shaped area appears. When a circular patch is not evident, a large area may be thinned and eventually killed by the pathogen. Examination of individual infected leaves reveals gray or tan irregular lesions with tan or brown borders. If conditions are only marginally favorable for disease development, only leaf lesions may develop. But if conditions remain favorable for disease development, entire leaves may be consumed.

To control brown patch disease in centipede and other warm season grasses (St. Augustine, Bermuda, Zoysia), avoid high nitrogen fertilization in the fall (mid-September to early December) or spring (late February to early June) when the disease is likely to appear. Several fungicides are labeled and provide good control especially when applied on a preventive schedule.

Dollar Spot is a persistent disease on several turfgrasses, and it occasionally occurs on centipede. Dollar spot is favored by warm, humid weather and is more severe on nitrogen-deficient turf and in dry soils. High humidity in the turf canopy favors fungal growth. When dollar spot fungi are active, tufts of fungal growth in small spots are frequently seen in early morning hours.

On closely mowed lawns, small patches of about one to two inches in diameter develop. On higher-mown turf, patches may exceed five or more inches in diameter. Individual diseased leaves exhibit characteristic lesions that are tan or bleached with distinct reddish-brown or purplish margins. Leaves may be girdled and collapse at the lesion even though the leaf tips remain green.

To control dollar spot disease a balanced fertility to avoid nitrogen deficiencies reduces disease severity. Irrigate during early morning hours to eliminate periods of high humidity and leaf wetness and to promote air circulation. Mow regularly at the correct height of cut. Several fungicides provide a good control but are generally unnecessary in home lawns. The expected time of occurrence for dollar spot disease is from mid-March to mid-July and from mid-August to early December.

Did you know that centipede grass is particularly well adapted to the sandy, acid soils of the southeastern United States? Its westward movement is somewhat limited by severe iron deficiencies that develop in the alkaline soils of the arid regions. And, its northward movement is restricted by low temperatures. Centipede grass is slightly more cold tolerant than St. Augustine grass, but extended periods of 5°F or less can kill centipede grass. It can be found throughout the West Indies, South America and along some areas of the west coast of Africa. It can be successfully grown in any of the areas where St. Augustine grass is adapted.


Have a question about any of your landscaping issues? Send your questions to:
Claude W. Blakely
Ask a Master Gardener
The Laurens County Master Gardener Association
P. O. Box 152
Waterloo, SC 29384-0152
cblakely@prtcnet.com