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By Sam Marshall
Cool, wet spring? Check. Susceptible turfgrass? Check.
If your lawn meets these requirements, then there is a chance you may have also dealt with a turfgrass disease known as large patch. Left untreated, it can ruin the aesthetic value of your lawn. While you may have heard it referred to as brown patch, this is a different disease altogether, as brown patch affects cool-season turf in warmer months, among several other differences.
Rhizoctonia solani is an old disease of warm-season turfgrasses and is most active during the fall months, when soil temperatures are below 70 degrees. However, symptoms might not be apparent until later in the spring months, when grass begins to green-up.
Symptoms are made worse and are more evident during cool, wet weather, much like we have experienced this spring. Other favorable conditions that encourage large patch and its spread include: excessive nitrogen fertilizer, excessive thatch, over irrigation and low mowing heights. All of the warm season grasses that are grown in this area are affected by large patch, but centipede is the most susceptible, followed by zoysiagrass, then St. Augustine, and Bermuda grass.
Large patch identification
While symptoms may vary depending on turfgrass variety and soil conditions, there are several telltale signs that indicate large patch. You may notice thinned areas of light brown grass that appears roughly circular in shape. The size of the affected areas will vary but can be anywhere from a few inches to a few feet in diameter. Upon closer inspection of individual leaves, the grass blades will appear tan to brownish in color, and contain a lesion-type wound along the sheath of the grass, which is the area just below the grass blade.
Controlling large patch in your lawn
To better understand how turfgrass disease gets into your lawn and causes damage, first imagine a three-legged stool, with “disease” being the seat and the “legs” being made up of a susceptible host, a pathogen and a hospitable environment in which the pathogen can grow and spread. If you remove any one of the “legs” from the stool, you can help prevent and control disease spread in your lawn. More technically, this is referred to as the disease triangle. Here are some tips on how to remove some of the “legs” from the stool and get better control of large patch in your lawn.
Generally, disease-resistant varieties of turfgrasses are recommended; however, there are currently no varieties of turfgrass that are immune to large patch. Bermuda grass appears to be the least resistant in that it will recover quickly after infection and treatment. However, it is still open to attack from large patch.
Preventing pathogens from entering your lawn is not practical, unless of course you have a lot of money and time that you want to devote to spraying and monitoring; however, you can take measures to keep pathogens under control when they appear. There are several fungicides available for large patch control, and a general rule of thumb is to make these applications around the first week of September (sometime around Labor Day), and then another application about a month later around the first of October.
Since large patch is a winter disease, your best window of opportunity to control it is during the fall months. Applications of fungicides during the spring will do little to prevent or control large patch spread. Synthetic fungicides containing azoxystrobin, often marketed as Heritage-G will provide control of large patch for one year. Remember to always read the label and follow the appropriate safety precautions when applying a fungicide.
While the cool, wet spring has created a perfect environment for large patch spread this year, you as the homeowner can help make your turfgrass an unfavorable environment for fungal pathogens. First, avoid irrigation when it is not necessary. When you water needlessly, you help to create a hospitable environment for turfgrass disease and encourage its spread.
Secondly, do not apply nitrogen to warm season grasses during the fall and spring. Because grasses are slow growing at this time, they do not require large amounts of nutrients. Since warm-season grasses have different nutritional requirements, you should have your soil tested so that you can make accurate and proper fertilizer applications.
Fertilizer applications should only be made around the time when grass is beginning to break dormancy (about three weeks in the spring) and before dormancy (about six weeks in the fall). You should avoid placing turf in low-lying areas that are consistently saturated and are poorly drained. As much as possible, try to control traffic on your lawn in order to mitigate soil compaction, which reduces water drainage. Proper mowing height and thatching are also recommended as cultural control measures to reduce the spread of large patch.
The only way to be sure you have large patch is to bring a sample of turf into your extension office and have it analyzed by an agent. For assistance with pest and disease turf management, contact your local extension office. In Brunswick County, call 253-2610.
To learn more about other consumer horticultural programs contact Sam Marshall, horticultural agent, at email@example.com. Call the Cooperative Extension office at 253-2610 or visit the Extension website at brunswick.ces.ncsu.edu.