Soil Temperatures Signal Turf Disease

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green lawn with large patches of brown

As fall approaches and temperatures decline, a very common turfgrass disease begins to affect grasses like centipede, zoysia, and St. Augustine. This disease, Large Patch (Rhizoctonia solani), creates areas of circular dead grass that can take several months to recover. As soil temperatures begin to dip below 80 degrees Fahrenheit, the disease pathogen (Rhizoctonia solani) becomes active and symptoms can appear.

Current symptoms may include circular areas in turf that have a reddish leaf color along with dying turf. As our warm season grasses go into dormancy, these spots will be difficult to see as all the individual leaf blades turn straw brown. However, the disease is still active until soil temperatures reach 50 degrees and will progressively enlarge these circular dead areas within your turf. In the spring as the grass breaks dormancy and begins new green growth, you will be left with a very noticeable area of dead turf.

Large patch disease is favored by cool temperatures and wet conditions. Areas in your yard that are prone to hold or channel water will usually be infected first; however, the disease can occur almost anywhere when conditions are favorable. You can make the disease worse by over fertilizing with nitrogen and with early or late season nitrogen applications in spring and fall. In general, nitrogen should not be applied to warm-season grasses within six weeks before dormancy in the fall or within three weeks after green-up begins in the spring.

A well-timed fungicide application in the fall before the disease becomes active can provide very good control. Timing of these applications should coincide with soil temperature. When soil temperatures dip to 80 degrees Fahrenheit for 4-5 days, application of a fungicide, especially to those areas of previous infection, will help prevent disease development. Common turf fungicides such as Bayer, Fertilome, Spectracide, and Scotts, have active ingredients (propiconazole, myclobutanil, azoxystrobin) that should provide adequate control. Refer to the label for specific directions on rate and turf type. For more information on available control options, visit the NC State Extension Turffiles website.

If you see evidence of the disease in the spring as your grass greens-up, applying a fungicide may help reduce the spread. However, as temperatures rise above 70 degrees Fahrenheit, the disease will become dormant and fungicide applications will not help the grass recover. By mapping these areas in the spring, you can provide a targeted fungicide application in the fall to help prevent reoccurrence.

Dead areas in the warm season grasses can be encouraged to fill back in by the rhizomes and stolons (runners). Proper fertility and weed management will help to encourage regrowth. Do not apply a preemergence weed control product in these areas, as many of our preemergence products inhibit root growth. New runners trying to grow back into these areas will have a difficult time rooting through these herbicide applications. Most grasses can fill back into damaged areas during one growing season. Wide spread applications of fungicides are generally not needed and can be quite costly. Just be familiar with the symptoms of this disease and keep an eye out for progression. If you have questions about this disease or other turf related issues, please feel free to contact Daniel Simpson at 252-745-4121 or daniel_simpson@ncsu.edu.

Written By

Daniel Simpson, N.C. Cooperative ExtensionDaniel SimpsonCounty Extension Director and Extension Agent, Agriculture - Horticulture Call Daniel Email Daniel N.C. Cooperative Extension, Pamlico County Center
Updated on Sep 15, 2021
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