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1C53 Take-all root rot: A fungal plant pathogen of warm

By Holly Thornton
University of Georgia

Volume XXXIII
Number 1
Page 25

In 2007, the University of Georgia Homeowner Integrated Pest Management Plant Disease Clinic saw a lot of turfgrass samples. Take-all root rot was the most frequent diagnosis for problems in homeowner lawns.

This turf pathogen, which was almost unheard of a decade ago, has now spread throughout Georgia. It’s a severe problem for warm-season grasses, especially St. Augustine and centipede.

The fungal pathogen responsible for the damage is Gaeumannomyces graminis var. graminis. Most simply refer to the problem as take-all root rot.

Symptoms of the disease are most prominent on lawns stressed by hot, dry weather like we’ve had the last several summers in Georgia. Initial symptoms of take-all root rot are patches in the turf that are circular to irregular, yellow to light brown and thinning. They can measure anywhere from 6 inches to 3 feet in diameter. As the disease progresses, patches may unite and reoccur in subsequent years, eventually killing large areas of the lawn.

When a homeowner notices symptoms in late spring or early summer, the fungus has likely caused extensive damage because it actually colonized and attacked the turf the previous fall. Many times, severely damaged areas will need to be reseeded or new sod planted.

As the common name infers, this is a root rot infection. A preliminary test for homeowners would be to tug on a blade of grass. If it pulls out of the soil without any resistance and there are little to no roots or the roots are blackened, shortened and rotted, then this could be an indication of take-all root rot infection. At this point, have the problem accurately diagnosed at a local county Extension office or by the Homeowner IPM Diagnostic Clinic.

Integrated management is the best approach to preventing and managing take-all root rot in home lawns. Since take-all root rot is associated with stressed lawns, take these disease-management steps:

  • Test the lawn’s pH. Maintaining a soil pH below 6.5, preferably between 5.5 and 6.0, will reduce the disease’s severity.
  • Provide adequate drainage. Core aerate the lawn in the spring to help reduce compaction.
  • Water once a week to a depth of 3-4 inches. This amount is sufficient.
  • Fertilize properly. This depends on the type of turfgrass and the site conditions, whether sunny or shady. For example, centipede lawns should only get a pound of nitrogen per year – a half pound each in the spring and fall.
  • Mow at the proper height for your particular turfgrass species.
  • Avoid applying herbicides to damaged areas of the lawn. St. Augustine, for example, doesn’t have a high tolerance for herbicides.
  • More recently, Texas A&M professor Phillip Colbaugh found that applying a sphagnum peat moss topdressing to St. Augustine grass has proven to reduce symptoms of take-all root rot in home lawns. Additional information can be found at http://dallas.tamu.edu/People/pcolbaugh/PeatmossPoster(051605).pdf.

    Lastly, fungicide applications in the fall (before dormancy) and early spring will prove to be most effective. Fungicides containing the active ingredients triadimefon or myclobutanil are available to homeowners at local retail garden centers for control of this disease. Remember to always read and follow label directions carefully when applying fungicides.

    (Holly Thornton is a homeowner integrated pest management specialist with the University of Georgia College of Agricultural and Environmental Sciences Department of Plant Pathology.)

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