If present, they are variable in size, shape, and color. Many other fungal diseases can also cause leaf lesions. Microscopic examination is often necessary to determine the cause of the problem. In the cool weather of autumn, the grass may begin to grow into these dead areas again. The disease, however, is likely to reappear in previously affected areas the following summer, and to increase in intensity.
Summer patch is less of a problem in cool summers with adequate rainfall.
The fungus, Magnaporthe poae , survives unfavorable conditions as mycelium in infected plant tissue or plant debris. Spread during the growing season occurs by the fungus growing between roots. Symptoms are not noticed until temperature increases very drastically during wet weather. The pathogen may be spread by infected plant material and mechanical equipment. The primary stresses that influence disease development include excesses of thatch, fertilizer, and turf canopy temperature, as well as incorrect timing of fertilizer applications, low mowing height, and pH extremes.