TOLEDO, Ohio – When encountering turf problems, such as a blotchy yellow color, most experts would say the best practice to follow is to figure out what the culprit is and how to treat the problem before applying a chemical treatment. This can be done by getting down on your knees and taking a good look at the blades of grass at the edge of the damaged area. This way you can see healthy plants, infected plants and even the dead ones all in one spot.
For instance, take a lawn that has round, yellow spots that are about two and a half inches across and appear during hot weather. Some patches of grass are matted down and may look like straw. After pulling out a fistful of turf, a white mold is noticed near the roots and many of the blades have brown spots or look like wet, flat straw.
According to turf experts, these clues point to a fungus called dollar spot. This fungus is common in areas with lots of thatch. Little dead spots about the size of a silver dollar will appear, which gives the fungus its common name. Dollar spot bleaches out the blades of grass and leaves dark brown, reddish-brown or purple lesions. These lesions will cut off the flow of nutrients to the grass and cause it to die. This is often a sign that a lawn needs fertilizer.
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PATHOGEN: Sclerotinia homeocarpa. PRIMARY HOSTS: Kentucky bluegrass, fescues, perennial ryegrass, bentgrass. PREDISPOSING CONDITIONS: Periods of warm days and cool nights from spring to late fall. Dollar spot is widespread and destructive to most turfgrass species. It has become troublesome in tall fescue, a species thought to be resistant to this disease. The symptomatic pattern of dollar spot varies with turfgrass species and management practices. Under close mowing, the disease first appears as small, circular, straw colored spots of blighted turf about the size of a silver dollar. With higher mowing and coarser textured grasses such as Kentucky bluegrass, perennial ryegrass or tall fescue, the straw colored blighted areas are 3 to 6 inches in diameter and tend to be irregularly shaped. Affected patches frequently coalesce and involve large areas of turf. Grass blades often have straw colored or bleached white lesions shaped like an hourglass, with leaves typically dying back from the tip. The hourglass banding on the leaves is often made more obvious by a definite narrow brown band, which borders the bleached sections of the hourglass from the remaining green portions. In tall fescue, however, the pathogen causes a die back from the tip and produces irregularly shaped leaf lesions with brown borders that are not usually hourglass shaped. When the fungus is active and moisture is present a fine, cobweb-like mycelium may cover the infected area during early morning hours. Dollar spot tends to be most damaging in poorly nourished turfs, particularly when humidity is high or a heavy dew is present. The disease, however, can be destructive to lawns fertilized in spring with water soluble nitrogen sources. Hence, like red thread, dollar spot is not exclusively a disease of poorly nourished turf. CULTURAL MANAGEMENT: An application of 1.0 pound of N per 1,000 square feet to poorly nourished turf stimulates recovery. Use primarily fall applied slow release nitrogen in balance with phosphorous and potassium. Apply limestone according to soil test recommendations. Schedule mowing early in the morning to promote the drying of foliage and leave clippings on the lawn. Avoid a drought stress situation by increasing mowing heights and controlling thatch and soil compaction. – Peter Dernoeden, professor in the department of agronomy at the University of Maryland, College Park. Sidebar reprinted from the March 1997 issue of Lawn & Landscape magazine. |
Tom Walker, greenskeeper at Inverness Club, Toledo, Ohio, said late summer and early fall is the peak season for dollar spot to show up in lawns. "It shows up in turf that is deficient in nitrogen," he said.
Dollar spot pops up when the conditions are right, such as hot days and cool nights. "It is important to water your lawn in the morning to wash off the night dew," said Walker. "This dew contains fluids from the grass that enhance the growth of the fungus. One turn of your sprinkler head is enough to wash these fluids off."
Ed Mitchell, golf course superintendent of the Legacy in Ottawa Lake, Mich., said keeping lawns fertilized can head off many turf problems. "Dollar spot can be raked out with a heavy garden rake. I don't like to use chemicals unless is its necessary. With dollar spot, you can increase your nitrogen levels and let the grass grow the fungus problems out."
Mitchell recommends applying a good quality fertilizer with a 2-1-2 ratio. Walker also recommends light fertilization over chemical treatments. "Potash sulfate works well to fight this fungus. A light water-soluble application of fertilizer will help the grass grow and quickly recover. Your lawn will look full and green in no time," Walker said.
To monitor growth of the fungus, Mitchell marks the problem area. "Paint a circle around the spots, then check it the next day," he explained. "If 12 spots turned into 24 spots overnight, the fungus is spreading rapidly and you may want to spray it with a fungicide."
Most of the time the grass will regenerate itself. The crown under the soil is still healthy. Healthy turf can crowd out many problems on its own.
Article adapted from information included in a Sept. 13, 2000, article by Kelly Heidbreder in the Toledo Blade (www.toledoblade.com).