Answer: Without details of your maintenance schedule (watering, fertilizing, mowing), it's difficult to diagnose the problems with your Bermuda grass. There is a fungal disease called Take-All patch which matches the description of the problem and it normally hits this time of year.
Take-all patch, caused by the fungus Gaeumannomyces graminis var. graminis, is a serious disease of both Bermuda and St. Augustine grass. When the disease is active, the first symptom is often a yellowing of the leaves and a darkening of roots. The area of discolored and dying leaves may be circular to irregular in shape and up to 20 feet in diameter. A thinning of the turfgrass within the affected area occurs as roots, nodes and stolons become infected and the plants decline. Unlike brownpatch, the leaves of take-all infected plants do not easily separate from the plant when pulled and the stolons will often have discolored areas with brown to black roots. The roots are sometimes so rotted that damaged stolons are easily pulled from the ground. Roots and stolons of brownpatch infected plants usually have a healthy appearance. Regrowth of the grass into the affected area is often slow and unsuccessful as the new growth becomes infected. During the stressful high temperatures of the summer months, the weakened, infected turfgrass will continue to decline.
The pathogen survives on infested debris and on infected perennial parts of living grass plants. When conditions are favorable (cool, moist weather), the fungus grows on the surface of roots, stolons, rhizomes, crown and leaf sheaths of the grass and then penetrates and infects the tissues. As the weather becomes warmer and dryer, the infected plants are stressed, and symptoms become more evident. The pathogen can be spread over long distances when infected plants or plant debris are transported mechanically. Infected sod may serve as a source of inoculum even if it shows no immediate symptoms of the disease.
Controlling take-all patch is not easy and much has yet to be learned about this disease. Control efforts should consist of both cultural and chemical methods. Good surface and subsurface drainage is important. Excessive watering can also favor development of take-all patch. Irrigating only when required to maintain good plant growth and vigor is suggested, and infrequent but thorough watering is preferred to frequent shallow watering.
Since the pathogen can survive on infested thatch, prevention of thatch build-up is suggested. Efforts to dethatch and to prevent thatch accumulation may prove helpful. If soil compaction exists, aerification will help to alleviate this condition and allow the grass to establish a deeper, more vigorous root system.
Before you apply a fungicide, take a sample of the problem to your local Cooperative Extension office for positive identification. Helpful folks there will diagnose the problem and suggest control options.
Best wishes with your lawn!
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