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Tennessee Turfgrass – Michael D. Richardson, Ph.D., Professor of Turfgrass Management and Physiology, University of Arkansas, Department of Horticulture

Warm-season grasses like bermudagrass and zoysiagrass are usually preferred in environments such as Arkansas, as they are more tolerant of heat, drought, insects and diseases compared to cool-season turfgrasses. However, that does not mean they are bulletproof! All of the major warm-season grasses used in the Natural State can have fungal disease problems and the most severe diseases are spring dead spot and large patch. Spring dead spot (SDS) is primarily a concern on bermudagrass, while large patch can infect all of our warm-season grasses. The University of Arkansas turfgrass program has evaluated various cultural and chemical strategies to control these diseases for many years and we continue to evaluate new products and practices that can be used to manage the diseases.

Spring Dead Spot (Ophiosphaerella herpotricha or O. korrae)

Spring dead spot is often observed on turf that has been established for several years and especially in lawns or sports turf with excessive thatch. Spring dead spot is considered a “perennial disease” which means that it will show up in the same spots or areas year after year if conditions are favorable. Spring dead spot is often more severe in areas that are over-fertilized and typically more severe in high pH soils (>6.0). In turf areas with heavy SDS pressure, changes in cultural practices are important for long-term disease management. Verticutting and core-aerification to encourage aggressive stolon and rhizome formation and rooting is beneficial for SDS management. This should be done when the turf is actively growing.

As the name implies, SDS symptoms appear as the bermudagrass begins to green-up (Figures 1 and 2), but infection and damage occurs in the fall and the winter. As such, fungicide applications in the spring of the year, after symptoms are observed, are ineffective and not recommended. Once symptoms are present, practices that encourage growth and recovery of the bermudagrass are the only way to reduce symptoms. Fungicide applications must be made in the fall of the year, approximately one month prior to dormancy, to effectively reduce disease symptoms in the spring. It is recommended that fungicide applications be made when one-inch soil temperature is between 60 and 80 degrees. Since the disease is infecting the stolons, rhizomes, and roots of the plant, fungicides should be applied in high volumes of water (up to 5 gal / 1000 ft²) to get the chemical into the zone of disease activity. In addition, it is helpful to irrigate the fungicide in with 0.25 inches of water if possible.

It is also critical to understand that fungicidal control of SDS is difficult and it may take two to three years until a fungicide program effectively controls the disease. In most cases, two applications of a fungicide in the fall will be required for effective control. Over the past few years, most of our chemical control trials have been conducted on either putting green turf or fairway mowing heights, but we have also done a couple of lawn trials. The best up-to-date list of fungicide control options can be found in the publication out of Kentucky and Rutgers called Chemical Control of Turfgrass Diseases (http://www2.ca.uky.edu/agcomm/pubs/ppa/ppa1/PPA1.pdf). Some of the most tested products with good activity against SDS include tebuconazole formulations such as Mirage Stressguard and Torque. Some products that have not been updated in that publication, but which have shown good results in our trials include Enclave (chlorothalonil + iprodione + thiophanatemethyl + tebuconazole), Kabuto (isofetamid), Velista (penthiopyrad), Headway (azoxystrobin + propiconazole), Lexicon (pyraclostrobin + fluxapyroxad), Xzemplar (fluxapyroxad), and Navicon (revysol).

Large Patch (Rhizoctonia solani, AG 2-2)

Large patch can infect all warm-season turfgrasses in Arkansas, including zoysiagrass, St. Augustine, centipedegrass, and bermudagrass. This disease is really favored by cool, wet conditions, especially in the spring of the year, and this spring was a petri dish for the disease (Figures 3 and 4 – page 14). Symptoms of large patch can also be observed in the fall, but the major symptoms occur in the spring after green-up of the turf. Although large patch will occasionally show up on bermudagrass in cool, wet springs, fungicide control is not recommended since the bermudagrass will rapidly recover from the injury once temperatures increase.

Similar to SDS, in order to effectively control this disease, preventative fungicide applications are critical. Because the disease becomes active as the turf is going into fall dormancy, fungicide applications must be made in the fall of the year to effectively prevent a disease outbreak. In cases where high disease pressure has been observed, it will generally require two applications of a fungicide in the fall followed by a third, spring application at 50–100% green-up of the turf to effectively control this disease. In cases where a preventative fall application has not been made and disease is occurring in the spring, a curative application can limit further spread of the disease and can encourage recovery of the damaged turf. As with spring dead spot, the best up-to-date list of fungicide control options can be found in the publication out of Kentucky and Rutgers called Chemical Control of Turfgrass Diseases (http://www2.ca.uky.edu/agcomm/pubs/ppa/ppa1/PPA1.pdf). Some of the best products for large patch control are flutalonil (formerly Prostar and now Pedigree), Heritage and Disarm (QoI fungicides), and tebuconazole formulations such as Torque and Mirage. Other products that have shown good results in our trials include Velista (penthiopyrad), Armada (triflozystrobin + triadimefon), and Tekken (Isofetamid and tebuconazole).

Both SDS and large patch can be difficult and expensive to control with fungicides, so it is always best to look at all of your cultural practices to make sure you are not encouraging more disease through mismanagement of fertility or irrigation. If you choose to implement a fungicide program, remember to rotate various chemical classes in your program to avoid any resistance issues. Also, be sure to read and follow all labels carefully, as many products mentioned above may be restricted to use on certain turfgrass sites such as golf courses.