A relatively new disease of St. Augustinegrass, Nigrospora stolon rot,
has resulted in serious deterioration of St. Augustinegrass. The disease
appears to girdle the stolon (stem or runner) of St. Augustinegrass and
deprive the stolon of water and nutrients. Leaves and stolons appear to
be under severe moisture stress and soon become totally desiccated.
The disease has been especially severe during dry spring and summer months. High temperatures and drought conditions favor development of stolon rot in St. Augustinegrass. Symptoms of the disease include dark brown lesions on stolons. As conditions favor the fungus, the lesions enlarge and eventually girdle the stolon. The girdling of the stolon stops the movement of water and nutrients to the leaves. The leaves soon wilt, turn yellow and die. New growth on the terminal end of diseased stolons is typically thin and yellow reflecting a limited supply of nutrients to the growing point. Overall symptoms are similar to those caused by chinch bugs on St. Augustinegrass.
Laboratory observations of stolons from diseased areas may show the presence of Nigrospora as well as Curvularia. Both fungal organisms are weak pathogens and usually only attack plants under stress. Environmental conditions such as unusually low winter temperatures, extreme drought and extremely high temperatures during spring and summer contribute to the occurrence of stolon rot. Providing adequate moisture, raising the mowing height and two applications of Daconil 2787 at 8 oz. per 1,000 sq. ft. at 14- to 21-day intervals has provided good control of the disease.