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Archive for Sunday, June 20, 2004

Brown patch endangers green lawns

June 20, 2004

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There is no doubt that the warm spring rains have been good for our gardens, flowers and lawns. They have quenched the thirst of our drought-stricken plants.

However, they also have given life to fungus and disease. If your lawn started out lush and green but has recently turned to patches of brown and tan, you may be victim of the turfgrass disease brown patch.

Brown patch is a summer disease of cool-season turfgrasses -- especially tall fescue. It is caused by the fungus Rhizoctonia solani. The fungus survives in thatch and soil as resting structures called bulbils. The disease begins to infect grass leaves when nighttime temperatures are above 70 degrees and the leaves stay wet for more than 10 hours. Brown patch can be active from May through mid-September.

Brown patch can develop rapidly; it only takes 24 to 48 hours for large areas of turf to become infected. Symptoms on tall fescue vary depending on weather and management practices. In some cases, the disease appears as distinct circular patches of blighted turf that range in size from a few inches to several feet in diameter. Patches initially are dark purple-green, but then quickly fade to light tan or brown as the diseased leaves dry out.

In most cases however, blighting tends to occur in a more irregular or diffuse pattern without formation of circular patches. Diseased turf may appear drought-stressed even though sufficient soil moisture is present. In most cases, the fungus only attacks the leaves, but during severe disease pressure, the crowns, or growing points, also may be killed.

Several cultural practices will slow brown patch development. Avoid seeding rates greater than six to eight pounds per thousand square feet when establishing new lawns. A high seeding rate results in an excess number of turfgrass plants that makes it easier for the fungus to move from leaf to leaf.

Next, do not overfertilize. Applications of more than four pounds of actual nitrogen per thousand square feet can result in increased brown patch activity. This is true even if the majority of the fertilizer is applied in spring and fall when the disease is not active. A light fertilization after a brown patch epidemic may speed recovery. But do not apply the nitrogen when brown patch is active because it will only prolong the disease. Do not bag the clippings when mowing.

Recent research has demonstrated that letting the clippings fall does not increase brown patch severity. Do not water the lawn in late afternoon or evening. This extends the time the leaves stay wet and increases the likelihood of brown patch development. Irrigation after midnight to mid-morning is preferable as these are the hours the turf would normally be wet from dew.

Several fungicides are labeled for control of brown patch on tall fescue. However, most are restricted use and can only be applied by a professional. Before applying a fungicide, consider whether the application is necessary.

In most cases, brown patch causes temporary injury to the lawn. Although initial damage is unsightly and often unacceptable to homeowners -- research indicates that the turf will usually fully recover in two to four weeks without fungicide treatments.

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