Cov e r S to ry
Spring Dead Spot and Large Patch —
Spring Diseases
that Need Fall Attention By Michael D. Richardson, Ph.D., Professor of Turfgrass Management and Physiology University of Arkansas, Department of Horticulture
W
arm-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 longterm 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.
12 • A r kansas T u r f g r ass • Fall 2019
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-todate 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
