Diseases affect turfgrass

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The past couple of weeks I have seen and heard of quite a few disease problems with turfgrass. As always, the grass that seems to be affected most is St. Augustine.

There are numerous turf diseases, but the one that has gotten worse the last few years is take-all patch (Gaeumannomyces graminis). The other one is large patch (Rhizoctonia solani). These diseases can look quite similar.

Some people think that if they have a turf disease, they can put a fungicide on it and presto! the disease is gone and the grass spreads back in. Fungicides will not do any good if you treat at the wrong time for take-all patch, however.

With both diseases, you get round to irregular patches of dead grass anywhere from 6 inches to 3 feet in diameter. As the disease progresses, patches might come together, eventually killing large areas of the lawn. With large-patch disease this time of year, the grass almost gets a bronze-looking halo in the infected areas.

The best way to distinguish between take-all and large patch is by pulling on a yellow or brown blade of grass. In most cases, the blade infected with large patch will give some resistance, whereas the turf infected with take-all patch will easily pull from the ground.

Also, the stolon infected with brown patch will not be brown/black as it will be with take-all patch.

Take-all patch causes affected stolons to be easily pulled from the roots because of the root rot that takes place. The roots of the grass will be blackened, shortened and rotted.

Good management of the lawn is the best approach to prevent either disease. Take-all patch problems are closely related to soil pH. Keep the pH level below 6.5. Fertilizers and natural rainfall are acidifiers. Manganese deficiency increases the severity of take-all, so supplements can be added. A premium fertilizer with micronutrients contains manganese.

To help prevent either disease, maintain good surface drainage on the lawn. Core aerate the lawn to allow better drainage and movement of air and water to the roots. This is especially needed on turfgrass growing in heavy clay soil.

Water your grass only when it needs it and avoid frequent, light irrigation to reduce the humidity. The less often you wet the grass the better. Water deeply, running the sprinkler sometime between midnight and before noon the next day.

Follow recommended fertilization practices, particularly nitrogen, for each grass. A soil test will let you know the fertility levels and give nitrogen recommendations.

Excessive nitrogen can make large patch worse.

Be careful when applying herbicides to the lawn. St. Augustine does not have a high tolerance for herbicides. This is especially true when the grass may have been damaged by chinch bugs.

Don’t let your grass build up a big thatch layer. It should be no more than 1-inch thick. A thick thatch layer is a haven for diseases to develop.

With large patch, it helps to increase the air circulation around the lawn. Shrub and tree barriers contribute to shade and lack of air circulation. Some pruning of limbs and foliage can help.

Fungicide applications can be helpful. With large patch, you can apply them anytime you see the fungus. But this is not true with take-all patch. Research has shown that fungicides do little good during the summer. The best time to apply them for take-all patch is during the last week of September or early October.

A good signal is when the night temperature drops to 55 degrees. Then reapply 28 days later. Watch it next spring after green-up and apply again if needed.

The best fungicides for either of these two diseases that are available to homeowners in most garden centers are ones that contain myclobutanil (Immunox, Fertilome F-Stop, Green Light Fungaway). Two others for large patch are thiophanate methyl (Scotts Lawn Fungus Control) and maneb (Hi-Yield Maneb Lawn & Garden).

REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.


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