March brings springtime, and with the warmer temperatures, vibrant colors in the landscape like the lawn. Many lawns in South Carolina are warm season, like bermudagrass, centipedegrass, and zoysiagrass, which will start to transition from a tannish-brown color to a new green color. But while we may get excited when the grass starts to green-up again in the spring, there are some instances where springtime diseases can create patches of persistent off-color turf.
If you have centipedegrass, seashore paspalum, St. Augustinegrass, or zoysiagrass, you may have heard of large patch disease. Large patch is a disease caused by Rhizoctonia solani, a fungus that can attack these warm season turfgrasses in the spring and fall when soil temperatures drop below 70 °F. In some cases, the fungus may infect in the fall, and symptoms may not be obvious until spring. The symptoms of large patch are, as the name implies, large patches of straw-colored turf (Figure 1). As for bermudagrass, spring dead spot is typically more detrimental than large patch. This disease is caused by multiple species of Ophiosphaerella, which are also fungi that attack the turf in the spring and fall when soil temperatures drop below 70 °F. Symptoms of this disease also appear in the spring as small (i.e., 6-12 inches) bleached dead spots in the turf that persist well into warmer weather, which can allow weed development (Figure 2).
Both of these diseases are typically worse in lawns that have excessive nitrogen, heavy thatch accumulation, and saturated soils during fall and spring infection periods. As for management, avoiding the contributing factors mentioned above are most critical. Limit fertilization to summertime when the turf is actively growing, avoid mowing too low, and try not to over-irrigate. Regular aerification can also help the root zone by reducing compaction, allowing for more oxygen, and infiltration with irrigation. Chemical controls can help mitigate both diseases, but fungicides are most effective when used preventively in the fall when soil temperatures favor pathogenic fungi. Be sure to refer to the HGIC links below and others for more information on how to keep your lawn green each year.