As warm-season turfgrasses continue to green up, diseases are rearing their ugly heads. The main culprit this time of year is a fungus, Rhizoctonia solani, that causes large patch disease in lawns. Large patch can infect all warm-season turfgrasses, but centipede, St. Augustine, and zoysia are particularly susceptible.
Large patch appears in roughly circular patches that are yellow, tan or straw-brown with orange-brown borders. The patches are initially 2 to 3 feet in diameter, but can expand up to 10 feet or more, as the name “large patch” indicates. Early in the morning, a grayish ring can be seen in the area where the diseased turfgrass and the healthy turfgrass meet.
Large patch occurs in the spring and fall when environmental factors are favorable. Favorable conditions include humid days with temperatures ranging from 75 to 90 degrees Fahrenheit and nighttime temperatures above 60 F. The higher temperatures and humidity lead to an extended period of leaf wetness.
In the last 60 days, the local weather station in Dearing, Georgia, has recorded eight days of rain, totaling 4.81 inches, with an average relative humidity around 70% and an average temperature of 68 F (average high of 80 F and average low of 55 F). This information was taken from the Georgia Automated Environmental Monitoring Network, which collects reliable weather information for agricultural and environmental applications.
Turfgrasses are also more susceptible when coming out of — or going into — dormancy. Therefore, spring and fall are the times of year the grass is most vulnerable because it is more stressed and not growing as actively.
The best way to protect turfgrass from disease is to properly manage it by following lawn care practice recommendations. More information on warm-season turfgrass identification and lawn calendars for season-appropriate practices are available from University of Georgia specialists on the GeorgiaTurf website. Follow these best practices, which are easier and cheaper than using fungicides, to mitigate turf disease in your lawn:
- Avoid high nitrogen rates on warm-season grasses in mid- to late fall or in early spring. The disease-causing fungus readily attacks the lush growth of grass that nitrogen promotes. Avoid fast-release forms of nitrogen fertilizer.
- Irrigate grass only when needed and to a depth of 4 to 6 inches — about 1 inch of irrigation water per week. Water early in the morning to reduce extended leaf wetness. This disease can spread fast when moisture is present.
- Avoid spreading disease to other areas. Remove clippings to prevent spread to other areas during mowing.
- Keep lawns mowed on a regular basis to the proper height for the grass species. Lower or higher than optimum mowing heights can increase disease severity.
- Provide good drainage for both surface and subsurface areas. Correct soil compaction with core aeration.
- Test the soil and apply lime and fertilizer according to the test recommendations. This will help promote good health and vigor. See UGA Cooperative Extension Circular 896, “Soil Testing for Home Lawns, Gardens and Wildlife Food Plots,” for more information.
Centipede, St. Augustine and zoysia are at peak growth when soil temperatures reach 65 F. In Columbia County, Georgia, the soil reaches this temperature in late April to early May. This is the optimum time to fertilize. This is especially true of centipede and St. Augustine grasses. When these turfgrasses are fertilized too early, they turn yellow from stress. The nitrogen in the fertilizer causes more shoot growth than the root system can support, which can cause large patch disease to develop.
If prevention is not an option and treatment is warranted, fungicide applications can help manage large patch. There are many fungicides on the market labeled for use on lawns, and most will aid in large patch management. In order for the fungicide to work properly, follow the directions on the product label.
A great resource for selecting turf fungicide products is the home and garden edition of the 2021 Georgia Pest Management Handbook. The handbook gives current information on the selection, application and safe use of these products. The home and garden edition also covers pest control around homes, on pets, for pests of home garden vegetables, lawns, fruits and ornamentals, and for pests of public health interest associated with our homes.
To order a $29.95 print copy of the home and garden edition of the 2021 Georgia Pest Management Handbook, visit the UGA Press website or Amazon.com. To order by email or phone, send a message to firstname.lastname@example.org or call 800-848-6224. A Kindle edition can be purchased for $22.49 at Amazon.com