Root rot disease creeping up in Louisiana lawns

BATON ROUGE — LSU AgCenter plant doctor Raj Singh says homeowners around the state are beginning to see an increase in take-all patch, also known as take-all root rot.
The disease is caused by the soilborne fungus Gaeumannomyces graminis var. graminis (Ggg). The fungus is frequently found in association with turfgrass roots without causing significant disease.
“Take-all patch disease can be quite destructive,” Singh said. “The aboveground symptoms appear after the root system has already been severely compromised.”
The appearance of these symptoms generally coincides with periods of several abiotic stresses.
“The initial symptoms of take-all root rot are generally visible as an overall yellowing, thinning or drought-stressed appearance of the turf,” Singh said. “Diseased roots are often short, dark-colored and somewhat brittle.”
The overall density of the root system is also greatly reduced. Affected stolons can be easily pulled out from the lawns.
“Careful examination of stolons and the base of the leaf sheaths with a hand lens may reveal the presence of the black strands of fungal mycelium on their surfaces,” he said. “If left untreated, large, irregularly shaped areas of turf may die.”
He said that symptoms caused by take-all disease can easily be confused with injury caused by chinch bugs.
The management of take-all root rot relies primarily on the use of cultural practices to relieve the abiotic stresses that triggered the disease and to modify the environment to make it less conducive for the pathogen.
These stresses include soil compaction and poor drainage, drought, improper mowing height, excessive thatch buildup and the overuse of herbicides.
According to Singh, it is also important to be sure that the soil pH is in the range 5.5-6.0 and to use slow-release, acidifying forms of nitrogen.
“Because we are actively trying to regrow roots, it is important to mow the grass at recommended heights, provide adequate potassium (potash) and avoid use of root inhibiting herbicides,” he said.
None of the fungicides that are readily available to homeowners are particularly effective in controlling this disease once it has become established.
However, those containing the active ingredient azoxystrobin, triadimefon or propiconazole may be beneficial when used as part of an integrated disease management program.
“Make sure to apply at least 1/4 inch of water to move the fungicide into the root zone where it is needed to protect roots,” he said.