We have received several home lawn samples in the clinic recently, showing a variety of common springtime diseases.
On a home lawn, dollar spot appears as round, mottled straw-colored spots up to six inches in diameter, which may coalesce into larger patches. Lesions on individual grass blades are light tan with reddish brown margins.
Ascochyta leaf blight
Ascochyta leaf blight causes large areas of straw-colored turf, where healthy leaves are interspersed with infected leaves. Individual leaf blades die back from the tips, and the diseased tissue often looks pinched compared to the healthy tissue. Lesions in the center of the blades may resemble those caused by dollar spot, but without the reddish brown margin typical of dollar spot lesions.
Leaf spot, also called melting out, causes large areas of diffuse, thinned grass. Individual grass blades have tan, oval spots of varying size, with dark brown borders.
Slime mold appears after very wet weather or heavy watering. Slimy white, gray, or yellowish masses form round to irregular patches in the lawn. When they dry, the masses form small round white, yellow, or gray powdery structures on the grass blades. Slime mold typically disappears on its own as it dries out, but this can be accelerated by raking the grass.
Management of these turf diseases depends on maintaining the basic health and vigor of the lawn. Start with resistant cultivars of grass. Avoid over-fertilizing in the spring, which may cause lush vegetative growth that promotes fungal growth. Mow at a height of 2 inches in spring and fall, but 2-1/2 to 3 inches in the summer and mow only when the grass is dry to avoid spreading the fungi that cause these diseases. Water the lawn before midmorning to allow the leaves to dry before evening. Core aerate in early spring or fall to minimize thatch. Following these guidelines can help to prevent disease problems.
When you send a turf sample to the Plant Disease Clinic
To send a turf sample, collect a chunk of turf at least six inches in diameter, including the underlying soil and root system. Collect the turf from the edge of the diseased area, so that the sample includes both healthy and diseased grass. Wrap the sample in dry paper towels or newspaper. Do not put it in a plastic bag and do not add water.
Background information is as important as the sample itself. Please describe in detail the situation and the site conditions, when symptoms first appeared, and your "best guess" as to what the problem is. Pictures of the overall lawn should be included. Following these guidelines will help to ensure that you get the most accurate diagnosis possible.
This article originally appeared in the 6/25/2004 issue.
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