How to scout, diagnose and treat summer patch

April 19, 2022 -  By
Experts say that when turf displays visible symptoms of summer patch, the damage is unfortunately already done. (Photo: PBI-Gordon Corp.)

Experts say that when turf displays visible symptoms of summer patch, the damage is unfortunately already done. (Photo: PBI-Gordon Corp.)

Generally, when lawn care operators (LCOs) first notice summer patch, they’ll discover wilted, thinned circular areas that ultimately become large and yellow — resembling straw.

Often appearing sunken, the circular or irregular patches range in diameter from a few inches to several feet.

“If a non-host species — such as ryegrass — is present, frog-eye symptoms may be observed, with healthy, non-host tissue in the center of the patch,” says Brian Aynardi, Ph.D., Northeast research scientist for PBI-Gordon Corp. “The pathogen begins infecting host plants when soil temperatures exceed 65 degrees Fahrenheit at the 2-inch depth in the spring. Yet symptoms aren’t observed until significant heat or stress are detected.”

Aaron Hathaway, technical services manager for Nufarm, advises keeping an eye out for dark brown roots, especially in fine fescue lawns and Kentucky bluegrass. He says older varieties of Kentucky bluegrass are more susceptible than some of the newer tolerant cultivars.

To reduce the risk of summer patch overgrowth, Aynardi and Hathaway offer the following tips.

Scout for rotting roots

Although summer patch is a difficult disease to scout for because its earliest symptoms occur in rhizomes, roots and stolons, it’s not impossible. Professionals must look for dark (at times blackened), rotting rhizomes, roots and stolons.

“Unfortunately, much of the damage to the roots may have already occurred by this stage of symptoms,” Hathaway says.

Aynardi agrees, adding that damage occurs during the infection process in spring and early summer.

“Since summer patch tends to reoccur in the same areas year after year, scouting is best utilized to plan for preventive applications with fungicides the following spring,” he says.

Diagnose through visualization

Hathaway recommends lawn management professionals look for weakened, wilted or yellowed turf in patches, particularly in early summer.

“Also, look for other grass species or weedy grasses within these patches that are unaffected, a clue that you’re dealing with a disease like summer patch that selectively affects turf species,” he says.
Aynardi says LCOs should only confirm summer patch on turf through visible dark mycelia, which travels on the surface of the plant’s rhizomes and roots.

“Diseased plants often have necrotic root systems that are black or brown in color. So a diagnosis should never be made by foliar symptoms alone,” he explains.

Treat with fungicides

Timing is everything as LCOs prepare to apply fungicides. Curative applications in the summer can reduce the pathogen, but the damage has already occurred.

“Time the first fungicide application on lawns where summer patch has been seen in previous years when soil temperatures reach 65 degrees (at a 2-inch soil depth) for three consecutive days,” Hathaway says. “A second application may be necessary a month after the first, or the first may be enough in some years.”

Combination products with two modes of action, especially demethylation inhibitors and strobilurin fungicides, applied three to four times on 21- to 28-day intervals, often provide professionals the best summer patch control, according to Aynardi.

“Applications must be watered in immediately following treatment too, with sufficient irrigation — typically with greater than 0.125 inches.”

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