Rhizoctonia large patch (also known as brown patch in cool-season grasses) is the most common and severe disease of all warm season grasses such as centipede grass, zoysia grass, bermudagrass and St. Augustine grass. This disease is caused by a soilborne fungal pathogen Rhizoctonia solani. We start seeing this disease in home lawns and commercial turfs in fall and spring when the grass enters or exits the winter dormancy. As we are approaching colder temperatures this fall and if the lawns get sufficient rainfall or irrigation, we might start seeing this problem soon in home lawns and commercial turfs.
Favorable Conditions
- Temperature of the thatch layer between 50 -70 °F
- Continuous moisture available for at least 48 hours.
- Poor drainage, shade, thatch, excessive irrigation
- High and untimely fertilizer application
Symptoms
- Circular patches of diameter ranging from 3 ft. to 26 ft.
- Grass leaves at the periphery of the patch appear bright yellow and/or orange in color.
- The patches may recur at the same spot and expand in diameter year after year.
- Leaf sheaths have water-soaked, reddish-brown or black lesions.
- Dieback from the leaf tip towards the base due to leaf sheath infection.
Management Strategies
- Irrigation: Do not over-irrigate the lawn. Most lawns would need only an inch of water applied once a week. Frequent deep irrigation that soaks the soil to a depth of 6″ – 8″ is better than the continuous shallow irrigation.
- Drainage: Install drainage tile in poorly drained soils. Reduce traffic to avoid compaction. Modify soil profile to increase porosity. In case of excessive thatch build up, core aeration might be necessary to improve soil drainage and increase air circulation.
- Remove shade by pruning or removing shrubs and trees.
- A soil test will give you specific fertilizer recommendations. The amount of fertilizer and timing of application is critical for healthy lawn. Do not apply nitrogen fertilizer when soil temperatures are consistently below 70 °F. Nitrogen fertilizers are not recommended in late Fall and early spring.
- Mowing height: Lower mowing heights may create favorable environment for large patch. Keep mowing height consistent and correct for the specific grass (common bermudagrass: 1 – 2 in., hybrid bermudagrass: 1 – 1.5 in., centipede grass: 1 – 2 in., St. Augustine grass: 2 – 3 in., zoysia grass: 1 – 2 in.).
- A fungicide application might be needed to control Rhizoctonia large patch. Reach out to UGA Dougherty County Extension at uge4095@uga.edu (or your UGA County Extension Agent) for the diagnosis of this disease and specific fungicide recommendations.
More information on this turfgrass disease is available in the UGA Extension publication “Identification and Control of Rhizoctonia Large Patch in Georgia“.
