Spring dead spot (Ophiosphaerella spp.) (SDS) of bermudagrass (Cynodon dactylon (L.) Pers. x transvaalensis Burtt Davy) is one of the most challenging diseases in the United States transition zone. Six projects were conducted from 2019 to 2022 to better understand the environmental, edaphic, and spatial distribution of SDS epidemics and to examine management strategies for SDS with chemical and cultural practices. A survey of 51 locations provided support of the geographic distribution of Ophiosphaerella species across the Mid-Atlantic United States. Ophiosphaerella herpotricha and O. korrae were isolated from the Mid-Atlantic region, yet O. narmari was not. Cultivars in which parent material originated from the midwestern United States had predominantly O. herpotricha and cultivars in which the parent material originated from the southeastern United States had predominantly O. korrae. In vitro and in situ fungicide efficacy screenings were conducted for O. herpotricha and O. korrae. Additionally, field studies were conducted to optimize fungicide applications and bermudagrass recovery from SDS. Results highlighted that, generally, O. korrae was less sensitive to fungicides than O. herpotricha; the fungicides isofetamid, mefentrifluconazole, penthiopyrad, and pydiflumetofen were generally the most efficacious against SDS; the different fungicide application methods deployed produced mixed results in their effect on fungicide efficacy against SDS with increased efficacy of tebuconazole against SDS with soil surfactant applications and post-application irrigation in certain scenarios; the optimal timing for fungicide applications for SDS was from 13-18°C with tebuconazole and 13-21°C with isofetamid; and nitrogen applications without cultivation practices in the late spring/early summer optimized bermudagrass recovery from SDS. Lastly, a geospatial survey study was conducted to determine the environmental and edaphic factors that influence SDS epidemics. Results were variable with numerous environmental and edaphic factors influencing SDS depending on the year and location; however, soil pH, soil potassium content, and thatch depth were among the most consistent and influential factors on SDS epidemics. Ultimately, these data improve our recommended strategies for successful SDS management. / Doctor of Philosophy / Spring dead spot is a damaging turfgrass disease that causes aesthetically displeasing symptoms and potential safety and playability concerns for pedestrians and athletes traversing turfgrass surfaces. This disease is caused by three fungal species, and the distribution of these species in the Mid-Atlantic US and the management of spring dead spot epidemics are not well understood. Studies were conducted from 2019 to 2022 to determine the geographic distribution of the species that cause spring dead spot in the Mid-Atlantic, best management strategies for spring dead spot with chemical and cultural practices, and factors in the environment and soil that influence spring dead spot epidemics. Results from the geographic distribution study showed that two of the three fungal species that cause spring dead spot were found in the Mid-Atlantic US, which has major implications on management strategies for the disease. The results from the studies focusing on best management strategies for spring dead spot with chemical and cultural practices highlight that the two fungal species found in the Mid-Atlantic US responded differently to fungicides, few fungicides suppressed the disease to an acceptable level, fungicide application methods provided variable suppression of the disease, optimal timing for fungicide applications was in the fall months when soil temperatures were between 13°C and 18°C, and nitrogen fertilization without cultivation optimized bermudagrass recovery from spring dead spot symptoms. Lastly, the study examining the environmental and soil factors that influence spring dead spot epidemics showed that many factors in the soil and environment influenced spring dead spot epidemics with soil pH, soil potassium content, and thatch depth among the most prevalent. These studies provide turfgrass managers and researchers a better understanding of spring dead spot and allow for more informed management decisions for prevention of and recovery from the disease.

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.