Cool, Moist Weather Promotes Lawn Diseases

Red Thread And Dollar Spot Thrive In Moist, Under-Fed Turfgrass

Jul 22, 2009

Turf diseases that favor cool, moist conditions are starting to appear in lawns, with the most common indicators being brown patches and red-colored grass blades.

Dollar spot and red thread are frequently to blame, but damage is often cosmetic, said Kevin Frank, professor of crop and soil sciences at Michigan State University.

“The diseases will usually not create enough damage that would require any fungicide treatments,’’ Frank said.

Disease Identification

Red thread and dollar spot are hallmarks of under-fertilized or slightly starved turfs, Frank said.

Red thread appears as pink or red discoloration on grass blades, eventually fading to a sandy color.

Dollar spot begins as tan markings the size of a silver dollar. Cobweb-like strands eventually form in diseased patches, but is actually a fine, white-colored fungus.

A close relative to dollar spot is brown patch. Irregular circle shapes of brownish turf develop with the outer edges taking on a grayish color.

Brown patch thrives in warm, wet weather, but unlike red thread and dollar spot, often forms in over-fertilized lawns, Frank said.

Favorable Conditions

“With the relatively good growing weather that we’ve experienced throughout much of the year, many of the fertilizer applications that were applied earlier in the season have probably run out and now the turf could probably use another fertilizer application,’’ Frank said.

Lawns watered late in the day, mowed too short or having excessive thatch build-up are susceptible to fungal diseases.

While there isn’t much we can do about the weather, watering early in the day so the lawn is dry by nightfall helps to keep fungal diseases in check.

Thatch May be a Factor

Thatch build-up of more than a half-inch may contribute to turf disease. Thatch is the accumulation of incompletely decayed vegetative materials at the base of the turf. Excessive thatch build-up can insulate the soil to the point where water and fertilizer do not reach the root zone.Grass may develop roots in thatch instead of developing deeper into the soil.

Restoring Turf Health

Changing mowing and watering practices in many cases will help resolve disease problems in turf.

Mowing lawns at a higher setting in summer helps the plant shade itself against heat and clippings left on the lawn returns nitrogen to grass plants.

A quick-fix for red thread and dollar spot is to apply a quick-release nitrogen fertilizer to encourage turf growth and to mask symptoms, Frank said.

“Cool temperatures should put the freeze on brown patch and will help stimulate turf grass growth to grow over the damage created by all these diseases,’’ he said.

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