Rhizoctonia Large patch of turfgrass is most common in the fall and in the spring as warm season grasses are entering or leaving dormancy. Large patch is caused by the soilborne fungus Rhizoctonia solani (AG 2-2LP). It can affect all warm-season turfgrass species. The disease produces irregularly-shaped weak or dead patches that are from 2 feet to up to 10 feet in diameter. Inside the patch, you can easily see brown sunken areas. On the edge of the patch, a bright yellow to orange halo is frequently associated with recently affected leaves and crowns. The fungus attacks the leaf sheaths near the thatch layer of the turfgrass.
Large patch disease is favored by:
- Thick thatch.
- Excess soil moisture and poor drainage.
- Too much shade, which stresses turfgrass and increases moisture on turfgrass leaves and soil.
- Early spring and late fall fertilization.
If large patch was diagnosed earlier in the season, fall is the time to prevent and manage it. Cultural practices are important in control of the disease. Without improving cultural practices, you may not achieve long term control.
- Use low to moderate amounts of nitrogen, moderate amounts of phosphorous and moderate to high amounts of potash. Avoid applying nitrogen when the disease is active.
- Avoid applying N fertilizer before May in Georgia. Early nitrogen applications (March-April) can encourage large patch.
- Water timely and deeply (after midnight and before 10 AM). Avoid frequent light irrigation. Allow time during the day for the turf to dry before watering again.
- Prune, thin or remove shrub and tree barriers that contribute to shade and poor air circulation. These can contribute to disease.
- Reduce thatch if it is more than 1 inch thick.
- Increase the height of cut.
- Improve the soil drainage of the turf.
Fungicides of the chemical groups carboxamides, benzimidazoles, carbamates, dicarboximides, DMI fungicides, di-nitro anilines, nitriles, polyoxins, and Qo inhibitors applied in late September or early October (night time temperatures deep below 65 F and or soil temperatures at 2-inch depth are below 70 F) provide LP control in Georgia. See the most recent Georgia Pest Management Handbook https://fieldreport.caes.uga.edu/publications/SB28/georgia-pest-management-handbook-commercial-edition/ or the Turfgrass Pest Control: Recommendations for Professionals https://turf.caes.uga.edu/publications/pest-control-recomendations.html. Depending on weather conditions, 1 or 2 fall applications can suppress disease to the point where spring treatments may not be required. Apply the fungicides in at least 2 (preferably 3) gallons of water per 1000 sq.ft. Water fungicides in is not required. Check fungicide labels for specific instructions, restrictions, special rates, recommendations and proper follow up and handling. More information on Rhizoctonia Large Patch https://fieldreport.caes.uga.edu/publications/C1088/identification-and-control-of-rhizoctonia-large-patch-in-georgia/
