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 / Spring dead spot (SDS) is one of the most devastating diseases of bermudagrass in Virginia. Bermudagrass is utilized as a playing surface on golf courses and sports fields. During the fall, when the bermudagrass is preparing for winter dormancy, SDS can infect and reduce the turf’s cold tolerance. As a result, dead patches are present in the spring of the year. SDS ruins the integrity of playing surfaces and is slow to recover. The objectives of this research were to develop SDS incidence maps, investigate methods to analyze these maps, and evaluate site-specific chemical applications to control SDS, based on historical incidence. We developed methods for building SDS incidence maps in 2016 and 2017. Maps were evaluated for spatial accuracy as well as their ability to differentiate SDS from healthy bermudagrass. Digital Image Analysis (DIA) was used to calculate SDS coverage. DIA utilizes pixel color values to distinguish SDS from healthy turf. In the fall of 2016 and 2017, a site-specific penthiopyrad (SSP) treatment was evaluated against two full-coverage, blanket fungicides in penthiopyrad (BP) and tebuconazole (BT), as well as an untreated control. These programs were analyzed and across three metrics, DIA, Patch Count (PC) and Patch Reduction (PR), the penthiopyrad treatments were statistically superior to both the tebuconazole and untreated. SSP compared favorably to BP for DIA, but blanket applications were statistically superior when analysis by PC and PR. SSP required 51% less fungicides in 2016 and 65% less in 2017 when compared to BP.

Spring dead spot (SDS), a monocyclic, soil-borne disease caused by Ophiosphaerella spp., affects the rhizomes and stolons of bermudagrass (Cynodon dactylon L. Pers), and is particularly severe in regions with extended dormancy, such as the transition zone. This research evaluates three aspects of SDS management: environmental influences, disease mapping, and the economic feasibility of precision treatments. To measure the relationship between local topography and SDS localization, UAV imagery was collected from 16 golf course fairways across three locations in Virginia and SDS coordinates were recorded. Using state lidar data, environmental factors such as slope, aspect, annual sunlight, and landform type were quantified. Generalized linear mixed-effects models revealed increased odds of SDS occurrence on north-facing slopes and landforms such as peaks and shoulders (p ≤ 0.001), while pits, valleys, and south-facing slopes were associated with decreased odds (p < 0.001). However, topographic features accounted for only 4.2% of the variance in disease distribution, indicating that other factors also play significant roles in SDS development. In parallel, precision treatment strategies (spot and zonal applications) were evaluated in a randomized complete-block design. Compared to full-coverage and untreated controls, precision treatments achieved similar disease control (p ≤ 0.001) while reducing the treated area by 48–52% (p ≤ 0.001), demonstrating a previously described Python script for spring dead spot detections efficacy in generating actionable disease maps. Finally, the economic viability of precision SDS management was assessed at the Independence Golf Club in Midlothian, VA. Cost analyses comparing precision and conventional treatments showed that a GNSS-equipped sprayer, used for precision applications, provided cost savings over a 10-year horizon when applying isofetamid or a combination product of pydiflumetofen + azoxystrobin + propiconazole. Conversely, this strategy was not cost-effective with annual applications of tebuconazole due to its low cost per application. These findings suggest that adopting precision treatment methods with appropriate fungicides can reduce costs and improve sustainability in SDS management. Together, these studies highlight the potential for integrating disease mapping, environmental analysis, and economic modeling to optimize SDS management strategies in turfgrass systems. / Doctor of Philosophy / Spring dead spot (SDS) is the most economically important disease of bermudagrass in the United States. It is caused by Ophiosphaerella spp. of fungi, which infect the horizontal growth structures of the plants causing damage in the fall leaving plants more susceptible to damage over the winter, these areas then fail to emerge from winter dormancy. Damage from SDS is often severe and long lasting making it important to avoid. While SDS has been well-studied, many important questions remain, including ways to improve management efficiency with fungicides and the reasons the disease develops where it does. To address questions on precision management we used a previously described Python script to build custom disease maps of SDS on golf course fairways. We looked at 16 fairways across 3 different locations in Virginia and treated them with either full-coverage applications, precision spot or zonal treatments based on the script, or left them untreated. Fairways treated with the spot and zonal treatments showed similar SDS suppression to full-coverage treatments the following year while using an average of 49% less fungicide. Next, we targeted concerns held by golf course superintendents. The first of these projects looked at the economic viability of these precision treatments over an entire golf course. To answer this, we recorded the amount of labor and money associated with precision treatments over an entire 18-hole course and found that the net present value over 10 years of purchasing a new GNSS sprayer for precision applications could be less than purchasing a new conventional sprayer for traditional applications. Finally, many golf course superintendents will say that SDS occurs more often on north-facing slopes. We looked at SDS locations in fairways that received little to no treatment previously and compared that to topography data. We found that while north-facing slopes and several other factors including the shape of the land itself were more likely to have SDS, the degree to which this is the case is not biologically relevant. These projects together highlight the complex nature of SDS and show that while its biology is complex, it is possible to control using precision turfgrass management techniques.