Spring dead spot (SDS) is the most destructive disease of bermudagrass and its hybrids, affecting intensively managed bermudagrass turf that is at least three years old. This bermudagrass disease is most prevalent in the United States where winter temperatures become cold enough to induce dormancy. The symptoms of SDS appear as sunken, necrotic patches of turf ranging from several centimeters to greater than 0.5 m in diameter. Field studies were conducted at Old Waverly Golf Club in West Point, MS on a Tifway bermudagrass fairway beginning January of 2005 and concluding December of 2006 to determine the frequency and the effects of soil temperature on occurrence of O. korrae in bermudagrass. Characterization of O. korrae isolates was conducted based on optimal in vitro growth temperatures and greenhouse pathogenicity studies. Cultural, nutritional, and chemical management practices were evaluated on the bermudagrass fairway for the reduction of SDS severity, promotion of improved turf color, quality, root health, and reduction of the thatch/mat layer. Treatments included core aerification with and without topdressing, vertical mowing, manganese, elemental sulfur, and myclobutanil fungicide applications. Each year was divided into seasons (winter, spring, summer, fall) based on the bermudagrass growth cycle in Mississippi. The frequency of O. korrae occurrence ranged from 14% in 2005 to 16% in 2006, and was similar for all treatments. Ophiosphaerella korrae occurrence was greatest in the winter and spring compared to the summer and fall. There was no direct association between mean soil temperature and frequency of O. korrae occurrence. Spring dead spot severity ratings were similar in 2005 and 2006. Vertical mowing had a significant effect on fall turf color in 2005 and fall turf color and quality in 2006. The aggressive cultural practices (i.e. vertical mowing, aerification) were the most consistent treatments for significantly reducing the thatch/mat layer and improving root health.

Spring dead spot (SDS) is the most destructive disease of bermudagrass (Cynodon spp.) in Virginia. SDS infects bermudagrass in the fall with symptoms appearing in the spring when dormancy breaks. Patches are sporadically distributed but generally reoccur in the same location. Chemical control options are expensive with inconsistent results. Our objectives were to develop SDS incidence maps, investigate methods to analyze these maps, and evaluate suppression efficacy of incidence-map-based chemical applications. Methods were developed to build SDS incidence maps in 2016 and 2017. 2016 SDS incidence maps were compared for spatial accuracy to Digital Orthophoto Quarter Quadrangle (DOQQ), ground-validated differential GPS coordinates, and to 2017 SDS incidence maps, with average deviations of 1.3 m, 1.6 m, and 0.1 m, respectively. Digital Image Analysis (DIA) of aerial maps was compared to a point-intersect method for validation with a significant linear relationship (r2 = 0.77, P ≤ 0.0001). In the fall of 2016 and 2017, a site-specific penthiopyrad (SSP) treatment was evaluated against blanket, full-coverage applications of penthiopyrad (BP) and tebuconazole (BT), and an untreated control. Treatments were compared using DIA, post-treatment SDS patch count (PC), and SDS patch reduction (PR). Across all three metrics, the penthiopyrad treatments were statistically superior to both the tebuconazole and untreated. SSP compared favorably to BP for DIA, but BP had 2.57 fewer PC (LSD = 2.05) and a greater PR by 2.58 (LSD = 2.55). SSP using SDS incidence maps required 51% less fungicides in 2016 and 65% less in 2017 when compared to BP. / Master of Science in Life Sciences