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Wet weather brings danger of fungal disease for lawns

Posted: November 15, 2015 - 12:04am

As warm-season lawns move into dormancy, disease has reared its ugly head.

The main culprit has been our miserable weather. In fact, in the last 30 days we have received 6.05 inches in Columbia County and out of those 30 days 15 have been rainy. According to the weather station in Dearing, Ga., we had an average high temperature of 72 degrees, an average low temperature of 55 degrees, with an average relative humidity of 80.9 percent. These conditions have produced the prefect environment for a fungus that causes large patch.

Large patch can infect all warm-season and cool-season grasses. Large patch appears in circular patches or rings that are yellow, tan or straw-brown with orange- brown borders. The patches are initially 2 to 3 feet in diameter, but can expand up to 10 feet or more. Early in the morning, a grayish ring can be seen in the area where the diseased grass and the healthy grass meet. Large patch occurs in the spring and fall when environmental factors are favorable. Late October and the beginning of November have produced perfect conditions for disease infestation. Turfgrasses are also more susceptible when going into dormancy. If you are seeing the disease, treatment is warranted.

The best way to prevent large patch in your grass is by following good lawn-care practices. Here are a few practices to keep in mind:

• Avoid high nitrogen rates on warm-season grasses in mid- to late fall or in early spring. The disease-causing fungus readily attacks the lush growth of grass that nitrogen promotes. Avoid fast-release forms of nitrogen fertilizer.

• Irrigate grass only when needed and to a depth of 4 to 6 inches (1 inch of irrigation water per week). Water from 11 p.m. to 5 a.m. to reduce extended leaf wetness. This disease can spread fast when moisture is present.

• Avoid spreading the disease to other areas. Remove clippings to prevent spread to other areas during mowing.

• Keep lawns mowed on a regular basis to the proper height for the grass species. Lower than optimum mowing height can increase disease severity.

• Provide good drainage for both surface and subsurface areas. Correct soil compaction by core aeration during the summer months. Prevent excessive thatch buildup. A pitchfork can be an excellent aeration tool.

• Test the soil this fall, and apply lime according to test recommendations. Disease may be more severe if the soil pH is less than 6.0

If prevention is not an option and treatment is warranted, fungicides can control this disease. There are many fungicides on the market labeled for use on lawns, and most will control large patch. This time of year applications of Azoxystrobin-Propiconazole(Headway$$$$), Pyraclostrobin- triticonazole(Pillar G$$$$) or azoxystrobin + tebuconazole (Strobe T$$$$$) would be the best. All of these are commercial products but can be purchased without a commercial pesticide license.

The down side is they are expensive. If price is a problem, visit a big-box store or one of our local hardware/garden stores and look for Myclobutanil(Ferti-Lome F-Stop$$) or Propiconazole(Bayer Advanced Fungus Control for Lawns$$) for a less expensive fungicide. In order for the fungicide to work properly, follow the directions on the product labeling.

After treatment, the patch should stop increasing. If the patch continues to increase, another treatment is needed. The grass then will fill in the areas affected by large patch next summer. A good rule of thumb on warm-season grasses, if the disease was present in the fall make a fungicide application in the spring. Typically, applications would be made mid- to late April but look for nighttime temperatures reach 60 degrees. Applications are made at 14- to 28-day intervals, depending upon the fungicide. Remember follow the directions on the product labeling to ensure control.

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