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Leaf Spot Disease of Lawns

As the name implies, leaf spot disease produces many symptoms. The symptoms you encounter depend on the weather patterns, the particular fungus involved and the variety of turf.

You will find occasional circular to elongated brown spots typical of the disease in every lawn. Don't be concerned about the occasional spots. Unless leaf spotting becomes heavy, this phase of the disease usually doesn't damage the lawn. However, the fungus can also attack the crown and basal parts of the plants, especially in the spring, cause extensive thinning and kill the grass. This is the serious stage of the disease. Sometimes it also attacks the root system, but this is less common in North Dakota. The disease attacks both bluegrass and fescues.

Look for reddish, purplish or brown drying and shriveling leaf sheaths as evidence of the disease. Do not confuse it with drought (check soil moisture conditions), insect damage or some mechanical problems.

Varieties differ greatly in susceptibility; many new varieties are resistant. In addition, you can greatly reduce the severity of attack by certain cultural practices. The first is mowing--cut high, 2 1/2 inches or above. Fertilize lawns of susceptible varieties primarily in the fall. Applying nitrogen heavily in spring increases disease probabilities. Watering should be deep, thorough and no more frequently than needed. Grass blades should dry quickly.

For those wishing to do so, fungicides can help protect the lawn and supplement cultural practices. The easiest chemical to apply is PCNB, sold as a granular and often with fertilizer. Apply it in the fall. It substantially reduces, though does not eliminate, the disease the next spring. Applying while the disease is active will do no good. There are also several fungicide sprays which can be applied at 10-day intervals for 4 or 5 times beginning about May 1. Look for chemicals on garden store shelves that are labeled for this purpose. Examples are Chipco 26019 and Daconil 2787.

It is also possible to overseed disease-thinned lawns with resistant varieties, such as Rugby, Parade, Adelphi and Vantage bluegrasses and Delray, Pennfire, Derby and Manhattan II Perennial rye grasses.

If you have more questions, please contact your county office of the NDSU Extension Service.

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