April 27, 2006

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OVERTON - Take-all root rot – a disease affecting St. Augustine lawns in particular – can be controlled, though it's an expensive proposition, said an expert with Texas Cooperative Extension.

"But if they (homeowners) have it now, they have to treat it now – right now – or wait until this fall," said Dr. Karl Steddom, Extension plant pathologist.

With severe infestations, take-all symptoms include large areas of yellowing and dying leaves, dead roots and the loss of a large percentage of the stolons, or runners. Take-all is also known as bermudagrass decline.

During certain times of the year, the disease may be confused with the symptoms of chinch bug infestations or brown patch, another plant disease.

But brown patch only kills the leaves – not the roots and stolons – and chinch bugs don't become active until hot weather, Steddom said.

"So if homeowners have large yellowing or bare spots in their St. Augustine lawns now (late April), the chances are very good that it's take-all," he said.

"Pull up some of the (yellowing) grass, and if the roots are dying, it's probably take-all," Steddom said.

Dead grass roots will be dark brown or black. Heathy roots will be white, he added.

The fungus that causes take-all is as ubiquitous as the virus that cause the common cold, Steddom said. As with the common cold, the symptoms aren't manifested unless the host – a warm-season grass in the case of the fungus – is put under stress. Take-all can infest other warm-season grasses, but it is most common in St. Augustine lawns.

"Stress in St. Augustine lawns usually comes from over-management; either applying too much lime at once, over-irrigating or applying a pre-emergent herbicide in the spring," he said. "St. Augustine is very sensitive to herbicides. If the label does not specifically mention St. Augustine, it's probably not safe to use it."

Steddom warned, treating now is going to be expensive and difficult. In the fall, it's much easier to treat with off-the-shelf products.

First, when treating this spring, forget using the prepackaged treatments for take-all found in home improvement stores and gardening centers. Only two of these "boxed" treatments are labeled for take-all and both contain the active ingredient myclobutanil, he said. If applied when temperatures are above 80 F, the chemical can stunt lawns.

"Once the temperatures have dropped below 80 F (in the fall) these products can be used safely," Steddom said.

It is possible to buy effective treatments for late spring applications from agricultural chemical distributors. Neither product requires a pesticide applicator's license to purchase or use. One product is Heritage; the other, Bayleton.

Because they are packaged for professional applicators, it won't be possible to buy a small amount of either, he said. Cost of the products will range from about $100 to nearly $400. The cheaper product will treat a couple of average-size lawns. The higher-priced one will treat a considerably larger area, and is cheaper per square foot to apply, Steddom said.

One package of either product will be sufficient to treat several home lawns, so the cost could be split with a neighbor, he said.

"The products need to get to the roots to work, so they should be applied with enough water to penetrate the soil 1-2 inches," Steddom said. "A garden hose sprayer or a small pump-up tank are not going to work."

This is because of the difficulty of accurately mixing extremely small amounts of chemical with large volumes of water.

Because of the difficulty in properly mixing and using expensive products, homeowners might want to hire a professional lawn care service, Steddom suggested.

If homeowners wish to verify with 100 percent certainty that they do have take-all, Steddom recommended sending a plant sample to the Texas Plant Disease Diagnostic Laboratory, part of Texas A&M University's Department of Plant Pathology and Microbiology.

Extension offices in all Texas counties will have the proper forms and be able to assist collecting, packaging and mailing the sample, he said.

The lab fee for routine testing is $30.

"Carefully follow label directions to a 'T' with all lawn-care products," Steddom said.

Overapplying the amount of lime called for by soil tests or improper applications of pre-emergent herbicides is just asking for the disease to get out of control again, he said.

"A fungicide treatment is not a silver bullet," he said. "It won't prevent take-all from coming back if the lawn is mismanaged."

Even with a spring application of fungicide, homeowners will see further damage as temperatures rise, he said. This is because the damage to the plant's root system has already occurred, and the plant can't take up water, even though the soil is wet.

"But a treatment will help lessen the damage,"Steddom said.

More information on take-all root rot in St. Augustine lawns can be found at http://tcebookstore.org/pubinfo.cfm?pubid=750 .