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Fungicides are routinely applied to golf course putting greens throughout the growing season. Gaining a better understanding of fungicide fate can improve fungicide use and stewardship. Therefore, optimizing fungicide applications with post-application management practices may enhance fungicide movement and limit potential off-target effects. Two field studies were initiated on a golf course putting green to evaluate the influence of post-fungicide application irrigation and mowing timing on fungicide movement into the soil profile and removal in turfgrass clippings. Plots were treated with a single application of either pyraclostrobin, triadimefon, or penthiopyrad and received 0.64 cm post-application irrigation immediately or 6 h after application or received no post-application irrigation. Clippings were collected 0, 1, and 3 d after treatment (DAT). Cores were harvested 0, 1, 3, 5, 7, and 14 DAT and dissected into the remaining aboveground vegetation (RAV; verdure/thatch; 0-to-2.5-, 2.5-to-5.1-, and 5.1-to-7.6-cm soil subsections). A small amount of fungicide (3.6%) was removed with clippings regardless of mowing and irrigation treatment. Post-application irrigation treatment influenced fungicide movement; however, 50% of fungicide remained restricted to the RAV for the first 3 DAT. Less fungicide remained restricted to the RAV, and more fungicide was detected in deeper soil depths when plots were irrigated immediately after application. Fungicide was only detected at the 5.1-to-7.6-cm depth when plots were irrigated immediately. Applying post-application irrigation immediately may result in more fungicide moving down to soilborne targets. Irrigating 6 h after application facilitated moderate fungicide movement compared with irrigating immediately but was better than no post-application irrigation.

Take-all root rot is a disease of ultradwarf bermudagrass putting greens caused by Gaeumannomyces graminis (Gg), Gaeumannomyces sp. (Gx), Gaeumannomyces graminicola (Ggram), Candidacolonium cynodontis (Cc), and Magnaporthiopsis cynodontis (Mc). Many etiological and epidemiological components of this disease remain unknown. Improving pathogen identification and our understanding of the aggressiveness of these pathogens along with growth at different temperatures will advance our knowledge of disease development to optimize management strategies. Take-all root rot pathogens were isolated from symptomatic bermudagrass root and stolon pieces from 16 different golf courses. Isolates of Gg, Gx, Ggram, Cc, and Mc were used to inoculate ‘Champion’ bermudagrass in an in planta aggressiveness assay. Each pathogen was also evaluated at 10, 15, 20, 25, 30, and 35°C to determine growth temperature optima. Infected plant tissue was used to develop a real-time PCR high-resolution melt assay for pathogen detection. This assay was able to differentiate each pathogen directly from infected plant tissue using a single primer pair. In general, Ggram, Gg, and Gx were the most aggressive while Cc and Mc exhibited moderate aggressiveness. Pathogens were more aggressive when incubated at 30°C compared with 20°C. While they grew optimally between 24.4 and 27.8°C, pathogens exhibited limited growth at 35°C and no growth at 10°C. These data provide important information on this disease and its causal agents that may improve take-all root rot management.

Repeated fungicide applications are typically required to provide adequate control of dollar spot on golf courses and may shift Sclerotinia homoeocarpa populations from sensitive to insensitive or resistant to an active ingredient. The objective of this study was to characterize the geographic distribution of fungicide-insensitive, fungicide-resistant, and multiple fungicide insensitive (MFI) S. homoeocarpa populations on golf courses in Pennsylvania and the surrounding region. S. homoeocarpa isolates (n = 681) were collected from 45 different golf courses or research facilities. Each isolate was evaluated in vitro against propiconazole, iprodione, boscalid, and thiophanate-methyl using discriminatory concentrations of 0.1, 1.0, 1,000, and 1,000 µg of active ingredient per milliliter of PDA, respectively. Relative mycelial growth (RMG) values were used to determine sensitivity or insensitivity based on comparison with a baseline population. Of the 681 isolates evaluated, 81, 80, and 85% exhibited reduced sensitivity to boscalid, iprodione, and propiconazole, respectively. A total of 41% of the isolates were resistant to thiophanate-methyl. Based on mean RMG of all isolates from each golf course, 16, 35, and 37 of the 45 golf courses exhibited reduced sensitivity to boscalid, iprodione, and propiconazole, respectively. A total of 585 isolates (86%) exhibited an MFI profile in which they were insensitive or resistant to at least two fungicides evaluated. Isolates with reduced sensitivity to boscalid, iprodione, and propiconazole, but sensitive to thiophanate-methyl, were the most common phenotype within the three-MFI profile. Fungicide insensitivity and resistance to commonly used fungicides, as well as MFI profiles, were prevalent in Pennsylvania and the surrounding areas and may cause management challenges.

Dollar spot is caused by the fungus Clarireedia jacksonii and is the most common disease of golf course turfgrass in temperate climates. Oxalic acid (OA) is an important pathogenicity factor in other fungal plant pathogens, such as the dicot pathogen Sclerotinia sclerotiorum, but its role in C. jacksonii pathogenicity on monocot hosts remains unclear. Herein, we assess fungal growth, OA concentration, and pH change in potato dextrose broth (PDB) following incubation of C. jacksonii. In addition, OA production by C. jacksonii and S. sclerotiorum was compared in PDB amended with creeping bentgrass or common plant cell wall components (cellulose, lignin, pectin, or xylan). Our results show that OA production is highly dependent on the environmental pH, with twice as much OA produced at pH 7 than pH 4 and a corresponding decrease in PDB pH from 7 to 5 following 96 h of C. jacksonii incubation. In contrast, no OA was produced or changes in pH observed when C. jacksonii was incubated in PDB at a pH of 4. Interestingly, C. jacksonii increased OA production in response to PDB amended with creeping bentgrass tissue and the cell wall component xylan, a major component of all walls of grasses. S. sclerotiorum produced large amounts of OA relative to C. jacksonii regardless of treatment and no treatment increased OA production by this fungus, though pectin suppressed S. sclerotiorum OA production. These results suggest that OA production by C. jacksonii is reliant on host specific components within the infection court, as well as the ambient pH of the foliar environment during its pathogenic development.

Clarireediasp. (formerly calledSclerotinia homoeocarpa), the fungal pathogen that causes dollar spot of turfgrasses, produces oxalic acid but the role of this toxin inClarireediasp. pathogenesis is unknown. In the current study, whole plant inoculation assays were used to evaluate pathogenesis ofClarireediasp. in various model hosts and investigate the role of oxalic acid in dollar spot disease. These assays revealed that both host endogenous oxalate content and pathogen-produced oxalic acid influence the timing and magnitude of symptom development. In time-course expression analysis, oxalate oxidase and related defense-associated germin-like protein genes in creeping bentgrass showed strong up-regulation starting at 48-72 hpi, indicating that germin-like protein genes are most likely involved in defense following initial contact with the pathogen and demonstrating the importance of oxalic acid inClarireediasp. pathogenesis. Overall, the results of these studies suggest that oxalic acid and host endogenous oxalate content are important for pathogenesis byClarireediasp. and may be associated with the transition from biotrophy to necrotrophy during host infection.