A problem with patches

COLUMBIA, Mo. – A lawn can be a source of pride when healthy and green, but a front yard full of disease can be an embarrassment.

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Dead-looking areas of the lawn can be the first sign of two common fungal diseases. Large patch of zoysia and brown patch on tall fescue showed up especially early this year thanks to above-normal temperatures in March followed by cool, wet weather.

“We saw some brown patch symptoms start in late March, which is highly unusual for this part of the U.S.,” said Lee Miller, a turf pathologist for University of Missouri Extension. “Cooler weather in April has slowed the disease, but the next warm spell will get it going again.” Meanwhile, that cool, wet weather has led to severe large patch outbreaks in zoysia, a warm-season grass that is coming out of winter dormancy and growing slowly.

For turf experts like Miller, there’s no easy answer in Missouri, which straddles vegetative zones, allowing both warm- and cool-season grasses to grow here.

“Missouri is in the transition zone, and our motto is, ‘We can grow any grass we want, we just can’t grow any of them very well,’” he said.

Brown patch and large patch are the two most devastating and widespread lawn diseases in Missouri. Brown patch in tall fescue appears as straw-colored areas about 2-3 feet in diameter, with leaf blades around the patch margins having characteristic tan lesions with dark-brown edges. Large patch, a closely related fungal disease, can afflict zoysia with 10- to 30-foot tan or grayish patches. When large patch is active, particularly after rainfall, the outer edges of patches will “fire” and leaves will turn a bright orange. The St. Louis area is seeing prevalent outbreaks of large patch this spring.

Homeowners can make things worse with ill-timed efforts to improve their yards. The biggest mistakes are often made with fertilizer.

“In May it’s way too late to feed a tall fescue lawn, and too early for zoysia, ” Miller said. “Cool-season grasses like tall fescue need fertilization in the very early spring and fall, and warm-season grasses like zoysia need to be fertilized in June, July and August. If you fertilize fescue or zoysia now with nitrogen, you will encourage lush leaf growth, causing the plant cells to bloat and become thinner. This makes it easier for large patch and brown patch fungus to infect.”

Weed-an-feed combinations sold at lawn and garden stores are also a bad idea right now. They contain enough nitrogen to exacerbate fungal pathogens while hurting plant health.

“If you have weeds like dandelions now, it’s vital not to use weed-and-feed products so you don’t encourage brown patch and other disease outbreaks in the summer,” Miller said. “Now you can use stand-alone products like Weed-B-Gon, Trimec or other three-way combination products.”

Another common mistake is trying to revive dying patches by watering. Fungal pathogens thrive on moisture.

“When areas begin to die out from fungal pathogens, you can actually kill them with kindness by overwatering,” Miller said. “It is crucial to not irrigate during the day or night, but instead water early in the morning. That way you rinse off the dew and guttation fluid that’s accumulated overnight, and suppress a brown patch epidemic.”

Find updates and other information on turfgrass and lawn diseases from University of Missouri Extension at www.turfpath.missouri.edu.