In the world of turfgrass, there are lots of fungi out there just waiting to colonize your lawn. From dollar spot to fairy rings, many turf diseases in Georgia are caused by fungi. Some fungal species prefer warm temperatures, while others like it cool. Regardless of temperature, most fungi like it moist and humid.
Allow me to introduce you to Rhizoctonia solani, the fungus that causes a disease called “large patch” when it infects warm-season turfgrasses, such as bermudagrass and zoysiagrass. Fun fact: when Rhizoctonia infects cool-season grasses, the resulting disease is called “brown patch”. Whether you have cool- or warm-season turfgrass, Rhizoctonia thrives when your lawn is over-fertilized and over-watered.
We see large patch during the spring and fall, when warm-season turfgrasses are entering or exiting their winter dormancy. Large patch is characterized by circular patches of diseased turf that can be less than 3 ft. and up to 25 ft. If you look at the blades of grass around the outer edge of the patch, they may look orange. Some patches may appear year after year, recurring in the same location and getting larger each year.
Rhizoctonia infects warm-season grasses on their leaf sheaths. If you look closely at the sheaths, you will see wet-looking, reddish-brown or black lesions. Leaf blades die back as a result of these leaf sheath infections.
So what can you do?
When it comes to plant diseases, prevention is always the cheapest and easiest approach. The best way to prevent large patch is to grow the healthiest turf you can! Avoid over-watering and over-fertilizing, both of which can stress your turfgrass.
Turf best management practices include:
- Take a soil test to measure the nutrient levels and pH of your soil.
- If prescribed in your soil test results, use low to moderate amounts of nitrogen (applied as slow release or over several applications), moderate amounts of phosphorous, and moderate to high amounts of potash. Do not apply any nitrogen after August or before May on warm-season grasses, and avoid applying nitrogen when the disease is active. Remember, Rhizoctonia loves an over-fertilized lawn!
- Most warm-season grasses like acidic soils, but diseases don’t. Maintain a soil pH around 5.5. You can make your soil more acidic by fertilizing with ammonium sulfate as a source of nitrogen.
- Water infrequently but deeply and only as needed. A good rule of thumb is to water once a week until soil is moist at a depth of 3-4″ OR water about an inch per week when rain is insufficient. Water in the morning if possible to avoid leaf wetness.
- De-thatch if your thatch layer is more than 1 inch thick.
- Avoid herbicide applications on areas of the lawn with disease symptoms.
- Increase your mowing height.
- Core aerate regularly to improve soil drainage. Remember, fungi like a moist environment.
Preventive fungicide applications also can help reduce disease. The best time to treat Rhizoctonia with fungicides is in the fall before warm-season grasses go dormant, a.k.a. when the fungus is most active. A spring fungicide application is the second-best time.
Keep in mind, fungicides alone may not solve turf diseases. Always read fungicide labels thoroughly, looking out for specific instructions, restrictions, special rates, recommendations, safe handling, and whether follow up applications are needed.
Don’t hesitate to reach out to your local UGA Extension office for recommendations. For more information, see our publication: Identification and Control of Rhizoctonia Large Patch in Georgia