(also called Rhizoctonia Blight)
Pathogen: Rhizoctonia solani
Turfgrasses Affected: All warm-season turfgrasses, especially St. Augustinegrass and zoysiagrass.
Occurrence: This disease is most likely to be observed from November through May when temperatures are below 80 F. It is normally not observed in the summer. Infection is triggered by rainfall, excessive irrigation or extended periods of high humidity resulting in the leaf canopy being continuously wet for 48 hours or more.
Symptoms/Signs: The fungus infects the leaf area closest to the soil, disrupting transport of water and nutrients to the upper portions of the foliage and eventually killing the leaf. A soft, dark rot will occur at the base of the leaf. The entire leaf will pull out easily from the leaf sheath due to this basal leaf rot. Eventually, entire plants will easily pull off the stolons. Roots are not affected by this pathogen.
This disease is often confused with phenoxy herbicide damage on St. Augustinegrass. Herbicide damage may cause the same overall symptoms of yellow or brown patches. The leaf may still pull out of the leaf sheath, but the base of the leaf is not dark and rotted. Instead, the leaf base is dry with a tan discoloration, and there is no distinct rotten smell.