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.

Large patch disease often becomes evident in the spring, as St Augustinegrass (above) and other warm season turfgrasses green up.
Matthew Zidek, Texas A&M AgriLife Extension Service, Bugwood.org

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 15^th in the Upstate and mid-state of SC, and no later than September 1^st 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 summer, as needed. Always irrigate the lawn in the early morning.

However, once this soil inhabiting pathogen has infected the turfgrass, it likely will take fungicide applications to help stop the disease. The fall is the most important time to apply curative fungicides to stop large patch disease, and the time to initiate treatments begins once the soil temperatures have dropped to 70 °F (see Table 1 for approximate times over SC).

Table 1. Timing of Fall Applications of Turfgrass Fungicides for Large Patch Disease Control in SC.

Spring Fungicide Application: A single fungicide application is required during the following spring once the turfgrass has begun green up. This is because the large patch pathogen is also active during this time.

Table 2. For Homeowner Use:

Best Turfgrass Fungicides for Large Patch Disease Control in Residential Lawns in SC.

For more information about lawn disease control, please contact the Clemson Home & Garden Information Center (HGIC). Proper lawn care will reduce the chance and severity of lawn diseases, and there are many helpful fact sheets on home lawn care on the HGIC website: https://hgic.clemson.edu/