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Abstract
Dollar spot, caused by Clarireedia spp., is one of the most problematic diseases of turfgrass worldwide. It diminishes functional and aesthetic quality of several turfgrass species by causing foliar blighting. Little is known about Clarireedia population dynamics in the southeastern U.S. Additionally, conventional control strategies, particularly repetitive fungicide applications, are costly and cause fungicide resistance issues. This work explores population structure and genetic diversity of C. monteithiana in Georgia turfgrasses and investigates the efficacy of UV-C radiation and oxygenated/ozonated nanobubble technology in controlling the disease. A total of 210 dollar spot isolates were obtained from various turfgrass hosts and locations throughout Georgia from 2019 to 2023, and C. monteithiana was identified as the most prevalent causal agent of dollar spot in the state. Genotyping-by-sequencing of 149 C. monteithiana isolates revealed population structure and genetic variability within the species through the detection of two genetic populations, both of which appear to reproduce clonally and evolve primarily through mutation. These findings emphasize the need for ongoing monitoring of C. monteithiana populations, as more diverse pathogens are better able to overcome common management strategies. Regarding UV-C radiation efficacy against dollar spot, daily low-dose applications significantly reduced pathogen mycelial growth and disease severity in in vitro and growth chamber settings, respectively. In field trials, a novel autonomous delivery system was used to administer UV-C treatments, resulting in significant reductions in disease severity over two growing seasons. Although UV-C was tested only against dollar spot in seashore paspalum, these results warrant further exploration of its effects against disease in other turfgrass species. In contrast, oxygenated and ozonated nanobubble water spray applications did not reduce dollar spot severity across multiple growth chamber and field trials, likely due to gaseous loss during application. Improving overhead spray technology to prevent this loss is likely necessary for these treatments to be effective in turfgrass. Despite these results, nanobubble aeration proved to be an efficient method for generating oxygenated and ozonated water treatments. Collectively, this work contributes to better understanding of C. monteithiana in Georgia and adds perspective to integrated dollar spot management through evaluation of novel control strategies.