(08/13/20) BATON ROUGE, La. — Take-all patch, also known as take-all root rot, is causing problems in some Louisiana lawns.
The fungus is frequently found in turfgrass roots without causing significant disease, said Raj Singh, LSU AgCenter plant doctor.
“This disease can be quite destructive as aboveground symptoms appear after the root system has already been severely compromised,” Singh said.
The appearance of these symptoms generally coincides with periods of several abiotic, or physical, stresses.
“The initial symptoms of take-all root rot are generally visible as an overall yellowing, thinning or drought-stressed appearance of the turf,” he said. “Diseased roots are often short, dark-colored and somewhat brittle.”
The overall density of the root system is also greatly reduced.
Affected stolons, or runners, can be easily pulled from 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.
Symptoms caused by take-all disease can easily be confused with injury caused by chinch bugs, Singh said.
The management of take-all root rot relies primarily on the use of management 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 build up and the overuse of herbicides.
It is also important to be sure that the soil pH is in the range of 5.5 to 6.0 and to use slow-release acidifying forms of nitrogen fertilizer.
“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,” Singh 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, he said.
“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,” Singh said.
Root systems of healthy (left) and diseased (right) turf. Photo by Raj Singh/LSU AgCenter
Presence of the black strands of fungal mycelium of the pathogen on affected grass stolons. Photo by Raj Singh/LSU AgCenter
Large, irregularly shaped areas of turf may die, and patches of bare ground appear. Photo by Raj Singh/LSU AgCenter