Institute of Food and Agricultural Sciences
Hendry County Horticulture News
Take-all Root Rot is Bad News
Take-all Root Rot is a disease of St. Augustine grass that often affects lawns at this time of year. The symptoms observed above ground are due to a soil borne fungus attacking the root system. By the time leaf symptoms are apparent, the root system has already been severely damaged.
Leaf symptoms will first appear in large irregular patches as yellowing of lower leaves accompanied by a decrease in leaf growth rates. Eventually, the lower leaves turn brown as they die. Other fungi may attack the grass and the affected turf will begin to thin. The final symptom is patches of dead grass. It is common for the patches to recover completely, however, these patches often appear year after year, expanding in size, as the pathogen moves via the root system from the initial infection site.
Take-all Root Rot is not simple to identify since other diseases, nematodes and insects can cause similar symptoms. The overall above ground leaf symptoms may look like Brown Patch caused by Rhizoctonia solani. With Brown Patch, the leaves will pull easily from the leaf sheath. Leaves will remain attached with Take-all Root Rot.
Pythium root rot may also cause similar symptoms. However, this disease normally does not kill the grass and is not as likely to occur in distinct circular patches. In addition, the turf will have an overall chlorotic appearance and not respond to nitrogen fertilization.
Nematodes will also cause a root decline and subsequent top growth decline. However, the roots will normally be simply discolored and malformed, but not black and rotted as is the case with Take-all Root Rot. Chinch bug damage may cause patches of dead grass, but chinch bug adult or nymphs will be present to confirm this pest.
All cultivars of St. Augustinegrass are susceptible to this fungus. This fungus prefers wet soil conditions and disease development will typically occur during the rainy season. Any factor that causes stress may predispose the lawn to attack by take-all root rot. Thus, cultural control methods are the best preventive and curative treatments.
It is important to reduce any factors that cause stress. Eliminate excessive irrigation. Mow the St. Augustinegrass at the proper height (no lower than 4 inches) and at the proper intervals so that no more than one third (1/3) of the leaf tissue is removed at each mowing. Mowing the turf too short will reduce leaf tissue which will reduce the root system. Scalping the grass is a major stress since you often damage stolons and crowns.
Drought stress before pathogen infection does not predispose the plant to disease. However, after the pathogen has infected the root system, drought stress will encourage disease symptoms.
Fertilizers may influence the disease by influencing soil pH. Acidifying fertilizers such as ammonium sulfate or slow-release urea products may be helpful. A lower soil pH will also encourage growth of soil microbes that may be able to biologically control the pathogen. Excess nitrogen may encourage development of the disease. Disease control will not be immediate with these cultural practices. It may take several years for the cultural practices to become effective in controlling Take-all Root Rot.
There are currently no specific fungicide recommendations because trials have not given consistent results. Systemic fungicides such as Banner and Bayleton, may be useful but only as preventative compounds applied weeks or months in advance of above-ground symptom development. Without eliminating the plant stresses via cultural control methods, fungicides will have minimal effects.
Replacing the sod is another alternative for control currently be recommended over the use of fungicides. It is necessary to remove the diseased sod and soil (6" deep) plus an area that is one to two feet beyond the symptomatic sod. However, there is no guarantee that new sod will not reintroduce the pathogen. Do not replant with slow-growing St. Augustinegrass cultivars as these cultivars will recover more slowly if infected. Avoid spreading known contaminated material into unaffected areas. Normal mowing will not spread the pathogen, but dethatching operations could spread the pathogen since infected root material could be moved by the machines.
In summary, attention to good lawn care practices will go a long way to reducing the impact of this potentially devastating disease. Good luck and good gardening.
Gene McAvoy is the horticulture agent with the Hendry County Extension Service. Direct your horticulture questions to PO Box 68, LaBelle, FL 33975, e-mail - email@example.com or phone 863-674-4092 or 863-983-1598. You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle. Office hours are from 8:00 - 5:00.
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