Johnny Morgan
Large patch, formerly called brown patch, is the most common disease of lawns in Louisiana. And it’s on the rise.
LSU AgCenter plant doctor Raj Singh said the disease can occur on all warm-season turfgrasses. It is particularly prevalent on St. Augustine grass.
“Symptoms appear as yellow, circular or irregular shaped patches of disease that can become quite extensive,” Singh said. “As the disease develops, large areas of turf appear brown as smaller patches come together.”
The pathogen does not kill the grass, but rather causes a rot at the base of the leaf sheaths, resulting in easy separation of leaves from the crown of the plant.
Large patch is caused by a soil-borne fungus Rhizoctonia solani. Optimal conditions for disease development occur when nighttime temperatures range from 60 to 75 degrees and daytime temperatures do not exceed 85 to 90 degrees.
“Free water on foliage is required for the disease to develop,” Sigh said. “The disease spreads rapidly on lawns with poor air circulation.”
One way to reduce disease incidence and accelerate turfgrass recovery is to maintain a healthy lawn through balanced fertilization, irrigation and regular mowing.
“Never apply more than 1 pound of nitrogen per 1,000 square feet per application, and always follow soil test recommendations for proper fertility,” he said.
Large patch symptoms are exacerbated with excess nitrogen application. Slow-release fertilizers with a balanced amount of nitrogen and potassium are recommended.
Irrigate lawns as early as possible in the morning while taking rainfall into account.
“Water deeply and as infrequently as possible without causing drought stress,” Sigh said. “Improve internal soil drainage and reduce compaction by aerating the lawn regularly.”
Minimize the amount of shade and improve air circulation over the lawn.
Raising mowing height will help the turfgrass recover. Do not mow lawns when wet, and mow diseased areas last because disease may spread to healthy areas with infected grass clippings.
Washing lawn mowers to remove grass clippings may also help reduce the spread of the disease.
“Excessive thatch can negatively affect turfgrass growth and provide a suitable environment for the pathogen,” Singh said. “Dethatching may be necessary to improve turfgrass growth.”
In addition to management practices, fungicide applications may be required to achieve effective disease control. Always apply fungicide at the rate and frequency listed on the product’s label.
Fungicides containing active ingredients such as azoxystrobin, myclobutanil, propiconazole and triadimefon may be used to manage large patch, he said.