Large Patch Disease Control in Warm Season Lawns

Large patch disease is probably the most common and damaging disease of warm season turfgrass in South Carolina. The most susceptible turfgrass to large patch is centipedegrass, followed by St. Augustinegrass and zoysiagrass. Bermudagrass lawns are not as severely affected because with proper care, this turfgrass can outgrow the disease problem. The pathogen causing large patch (Rhizoctonia spp.) is more active in the soil during the fall after temperatures have dropped from the summer‘s heat and again in the spring as turfgrasses green up.

Initially, the symptoms in the lawn are circular areas that may be more yellow or orange. As the disease spreads, it infects and rots turfgrass roots, stolons (above ground runners), and the leaf sheaths (the site where leaves are attached). Soon the turfgrass begins to die, and the pathogen moves outward expanding the diseased site. The dying areas may have a smoky brown perimeter where the fungus is active.

The conditions that favor turfgrass infection are excessive nitrogen applications in early spring and fall, watering the lawn too frequently, mowing the lawn too low, allowing the thatch layer beneath the turfgrass to build up, and having a poorly drained lawn. Correcting these conditions may be sufficient to prevent large patch disease and aid in control if it occurs. Fertilizers should not be applied to warm season lawns after August 15th in the Upstate and mid-state of SC, and no later than September 1st along the coast. Please note that most winterizer fertilizers also contain nitrogen, and they, too, must not be applied after these dates. Reducing irrigation frequency helps significantly. Water no more than once per week in spring and fall, and only once or twice per week in