@article{stephens_gannon_cubeta_kerns_2024, title={Influence of fungicide selection and application timing on take-all root rot management under field and greenhouse conditions}, volume={10}, ISSN={["2374-3832"]}, DOI={10.1002/cft2.20261}, abstractNote={Abstract Take‐all root rot (TARR) is a detrimental disease of ultradwarf bermudagrass ( Cynodon dactylon × Cynodon transvaalensis ; UDB) putting greens frequently diagnosed where warm‐season grasses are grown. Since this disease is largely aggregated and variable under field conditions, field research is difficult and often yields inconsistent results. Multiple pathogens have only recently been associated with this disease, so practical management solutions such as fungicide efficacy and fungicide application timing have not been thoroughly investigated. Therefore, the objectives of this research were to determine the influence of fungicide selection and fungicide application timing on take‐all root rot management under field and greenhouse conditions. In general, fungicides from the quinone outside inhibitor and/or demethylation inhibitor chemical classes provided the greatest reduction in take‐all root rot severity. Fungicide applications that were made when soil temperatures were between 77–86°F provided the greatest disease suppression. The in vivo greenhouse method developed in this research proved to be an efficient and consistent method to evaluate management practices such as fungicide efficacy on take‐all root rot. This research improves our understanding of fungicide efficacy and fungicide application timing for take‐all root rot management on ultradwarf bermudagrass.}, number={1}, journal={CROP FORAGE & TURFGRASS MANAGEMENT}, author={Stephens, Cameron M. and Gannon, Travis W. and Cubeta, Marc A. and Kerns, James P.}, year={2024}, month={Jun} }
 @article{stephens_gannon_thiessen_cubeta_kerns_2023, title={In Vitro Fungicide Sensitivity and Effect of Organic Matter Concentration on Fungicide Bioavailability in Take-All Root Rot Pathogens Isolated from North Carolina}, volume={24}, ISSN={["1535-1025"]}, DOI={10.1094/PHP-08-22-0072-RS}, abstractNote={ Take-all root rot (TARR) of ultradwarf bermudagrass is caused by Gaeumannomyces graminis (Gg), Gaeumannomyces graminicola (Ggram), Candidacolonium cynodontis (Cc), and Magnaporthiopsis cynodontis (Mc). Multiple pathogens have recently been associated with this disease, and biological parameters such as fungicide sensitivity have not been explored in ultradwarf bermudagrass. Although fungicides are commonly used to mitigate disease development, high organic matter present in the turfgrass system could limit the bioavailability of fungicides. Fungicide bioavailability can be influenced by organic matter concentration, and the physicochemical properties of fungicides could provide insight into their binding affinity. However, the influence of organic matter content on fungicide bioavailability has not been investigated. Therefore, the in vitro sensitivity of Gg, Ggram, Cc, and Mc to 14 different fungicides across three chemical classes was determined. An in vitro bioavailability assay was developed using three fungicides and three organic matter concentrations. Generally, demethylation inhibitor and quinone outside inhibitor fungicides provided the greatest reduction in mycelial growth, whereas succinate dehydrogenase inhibitors did not reduce mycelial growth. These data can serve as a foundation for TARR pathogen sensitivity to inform in vitro fungicide sensitivity studies and field efficacy trials. Pyraclostrobin and propiconazole have a high affinity to bind to organic matter, which was evident as more fungicide was required to inhibit Gg growth as organic matter concentration increased. This was not observed when evaluating azoxystrobin, which has a lower binding affinity. Understanding how TARR pathogens respond to fungicide in vitro and how organic matter concentration affects in vitro sensitivity will improve fungicide selection for management of TARR. }, number={2}, journal={PLANT HEALTH PROGRESS}, author={Stephens, Cameron M. and Gannon, Travis W. and Thiessen, Lindsey D. and Cubeta, Marc A. and Kerns, James P.}, year={2023}, month={Jul}, pages={162–170} }
 @article{stephens_gannon_cubeta_sit_kerns_2022, title={Characterization and Aggressiveness of Take-All Root Rot Pathogens Isolated from Symptomatic Bermudagrass Putting Greens}, volume={112}, ISSN={["1943-7684"]}, DOI={10.1094/PHYTO-05-21-0215-R}, abstractNote={ 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. }, number={4}, journal={PHYTOPATHOLOGY}, author={Stephens, Cameron M. and Gannon, Travis W. and Cubeta, Marc A. and Sit, Tim L. and Kerns, James P.}, year={2022}, month={Apr}, pages={811–819} }
 @article{stephens_kerns_ahmed_gannon_2021, title={Influence of post-application irrigation and mowing timing on fungicide fate on a United States Golf Association golf course putting green}, volume={6}, ISSN={["1537-2537"]}, DOI={10.1002/jeq2.20249}, abstractNote={AbstractFungicides 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.}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Stephens, Cameron M. and Kerns, James P. and Ahmed, Khalied A. and Gannon, Travis W.}, year={2021}, month={Jun} }
 @article{rioux_stephens_koch_kabbage_kerns_2021, title={Identification of a tractable model system and oxalic acid-dependent symptom development of the dollar spot pathogen Clarireedia jacksonii}, volume={70}, ISSN={["1365-3059"]}, DOI={10.1111/ppa.13319}, abstractNote={AbstractClarireedia jacksonii causes dollar spot disease of cool‐season turfgrasses in the United States and produces the phytotoxin oxalic acid. The role of oxalic acid in host–pathogen interactions of C. jacksonii is unknown and there are multiple challenges to studying these interactions in natural turfgrass hosts. Consequently, identification of model plants to study C. jacksonii–host interactions and the role of oxalic acid in pathogenesis is necessary. Controlled environment inoculation assays were used to evaluate pathogenesis of C. jacksonii in various model plants and investigate the role of oxalic acid in symptom development. Observations at microscopic and macroscopic levels demonstrated that infection progressed similarly in all monocots tested (creeping bentgrass, wheat, barley, rice, Brachypodium distachyon) but not in the dicot Arabidopsis thaliana. Plant oxalic acid content increased from near zero to around 0.2–0.4 mM following inoculation with C. jacksonii in creeping bentgrass, barley, and wheat. Conversely, oxalic acid content remained near zero in A. thaliana and was not well correlated with inoculation in rice and B. distachyon, both of which had higher endogenous oxalic acid levels than other monocots. Time‐course oxalic acid quantification experiments with creeping bentgrass and B. distachyon further supported a link between symptom development and in planta oxalic acid content and identified 48 hr postinoculation as a critical time‐point for investigating the role of oxalic acid in C. jacksonii pathogenesis. These studies demonstrate that various monocots can serve as tractable model systems for studying C. jacksonii–host interactions and that increases in oxalic acid content are associated with C. jacksonii symptom development.}, number={3}, journal={PLANT PATHOLOGY}, author={Rioux, Renee A. and Stephens, Cameron M. and Koch, Paul L. and Kabbage, Mehdi and Kerns, James P.}, year={2021}, month={Apr}, pages={722–734} }
 @article{townsend_rioux_kabbage_stephens_kerns_koch_2020, title={Oxalic Acid Production inClarireedia jacksoniiIs Dictated by pH, Host Tissue, and Xylan}, volume={11}, ISSN={["1664-302X"]}, DOI={10.3389/fmicb.2020.01732}, abstractNote={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 grass cell walls. 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’s 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.}, journal={FRONTIERS IN MICROBIOLOGY}, author={Townsend, Ronald V and Rioux, Renee A. and Kabbage, Mehdi and Stephens, Cameron and Kerns, James P. and Koch, Paul}, year={2020}, month={Aug} }