Fall Fungus Making Spring Debut Observes Horticulturist

Thomas J. Koske, Hollier, Clayton A.  |  10/4/2004 4:24:25 AM

News Release Distributed 03/24/03

Brown patch is showing up in some spring lawns. Although more common in fall, the disease is emerging from a combination of rain, humidity and higher temperatures, according to LSU AgCenter horticulturist Dr. Tom Koske.

Brown patch is the most widespread of all the turfgrass diseases. It occurs in all areas where turf is grown, and it attacks all known turfgrasses. The disease is characterized by the development of irregular, circular patches from a few inches up to several feet in diameter.

"These areas may have a brownish to grayish discoloration. Sometimes, but not always, a narrow, dark, smoke-colored ring may border the diseased areas," says LSU Ag Center plant pathologist Dr. Clayton Hollier. "The leaves in these affected areas are more or less water-soaked and blackened, and finally collapse and usually die."

The brown patch fungus generally attacks the base of turfgrass leaf sheaths where they are joined to stolons, but the roots and the growing points of the shoots are not usually killed. These water-soaked or scalded spots in the lawn can spread quickly, becoming large brown areas.

"This fungus occurs more frequently in lawns surrounded by trees, which reduce the circulation of air," Hollier says. "Brown patch is quite severe on St. Augustine in the fall, especially when temperatures are 60 to 75 degrees Fahrenheit. At temperatures above 90 degrees Fahrenheit and under low moisture conditions, fungal activity decreases."

Brown patch also occurs on bent bermuda, fescue, centipede, carpet and zoysia grasses. Several factors make grass more susceptible to brown patch, including:

  • Excessive applications of nitrogenous fertilizer in late summer and early fall, which promotes soft, tender, lush growth of grasses.
  • Watering in the late afternoon, which allows the micro-climate of the grass to remain warm, wet and humid for long periods.
  • Allowing thatch to build up. "Thatch creates a favorable environment for the development of the pathogen and, at the same time, creates an unfavorable environment for the lawn," Koske says.

You may begin to deal with brown patch now, according to Hollier. "Do not fertilize with nitrogen fertilizer," the plant pathologist says, explaining, "That will only make the brown patch worse." If you decide to use a fungicide, use a formulation that is mixed with water and applied, and do not use a granular material. Sprayed materials work faster in an existing disease situation.

Several turfgrass fungicides will do a good job, according to Hollier. They include those that contain the following active ingredients: azoxystrobin (Heritage), chlorothalonil (Daconil, Echo, Manicure), iprodione (26019), PCNB (Terraclor, Defend, Engage), thiophanate methyl (3336, Systec 1998) or triadimefon (Bayleton).

"If you find another brand of turf fungicide with the same active ingredients, use it if it is available," Hollier says, adding, "Go by label directions for rate and timing."

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