Description:

Initial activity of the fungus on the roots will only be observed by looking at the roots. If the turfgrass is not stressed or under low levels of stress, leaf symptoms may never be observed. However, under high stress conditions, symptoms will begin to appear on the leaves. By the time the leaf symptoms appear, the pathogen has been active on the roots for at least 2-3 weeks, probably longer.

Initial symptoms above-ground are irregular, yellow (chlorotic) or light green patches ranging in diameter from a few inches to a few feet. Roots will initially be thin and off-white in color with isolated black lesions. Eventually, roots will become very short, black and rotted. Stolons and rhizomes may have black lesions and, under severe disease conditions, begin to rot. Entire plants may die resulting in irregular patches of thinning grass, and if not controlled, bare patches may develop. Using a microscope, black strands of fungi (runner hyphae) will be present on outside of roots, stolons and rhizomes, as will special structures called hyphopodia.

Control:

This disease is very difficult to control once the aboveground symptoms are observed. Therefore, measures that prevent or alleviate stress are the best methods for completely controlling the disease or at least decreasing the potential damage. Stress on turfgrass can result from many factors.

The turfgrass must be mowed at the correct height during the summer. It may even be necessary to raise the mowing height during periods of conducive weather. The turfgrass must be mowed as frequently as necessary so that only one third (1/3) of the leaf tissue is removed during any one mowing event. Scalping the grass damages the growing point.

When the disease is active, frequent foliar (leaf) feeding of all nutrients (N, P, K and micronutrients) in small amounts will be necessary if the root system is severely damaged. The roots are not functioning properly, and so will not be able to efficiently obtain nutrients from the soil.

Please check the "Extension Agents' Handbook of Insects, Plant Disease and Weed Control".