Golf Course Management

SEP 2018

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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09.18 GOLF COURSE MANAGEMENT 79 CUTTING EDGE Teresa Carson Nitrogen fertilization affects dollar spot severity in bentgrass Dollar spot is the most economically im- portant disease of golf course turfgrass in North America. Previous research has shown that nitrogen fertilization may reduce dollar spot severity, but the results have been mixed, and the impact of nitrogen on the dollar spot pathogen's production of the virulence factor oxalic acid is unclear. e objectives of this study were to evaluate the impact of nitrogen fertilization on dollar spot severity in the field and to determine how oxalic acid production is influenced by nitrogen and ambient pH in vitro. A three-year field trial was initiated in spring 2015 to test the impact of four differ - ent nitrogen rates (4.35, 8.70, 17.32 or 26.13 pounds nitrogen/acre [4.88, 9.76, 19.42 or 29.29 kilograms/hectare]) on Penncross creep - ing bentgrass maintained at putting green height at locations in Madison, Wis., and Glenview, Ill. e in vitro assays measured oxalic acid production and pH change of two S. homoeocarpa isolates grown in potato dex - trose broth (PDB) media. Results from the field trial indicated that, at the highest ni - trogen rate of 26.13 pounds/acre, dollar spot suppression was comparable to that of a fun - gicide program, while the lower nitrogen rates were comparable to the non-treated control. In vitro results demonstrated that the fungus produced more oxalic acid when initial PDB pH was 7 compared to an initial pH of 4. is research demonstrates that nitrogen fertiliza - tion alone can provide effective dollar spot suppression and that the fungus may produce oxalic acid to create a more favorable pH for fungal infection. Future techniques altering the production of oxalic acid through nitro - gen fertilization and other cultural practices may lead to novel management strategies for this important disease. — Ron V. Townsend and Paul L. Koch, Ph.D. (, University of Wisconsin-Madison, Madison, Wis.; and Edward J. Nangle, Ph.D., Ohio State University ATI, Wooster, Ohio An earlier version of this summary was published in the 2017 ASA-CSSA-SSSA Meeting Abstracts, ASA, CSSA and SSSA, Madison, Wis. Neonicotinoids vs. white grubs Neonicotinoids are the most popular in- secticides used in turfgrass management worldwide, and they have been a mainstay in the management of white grubs in cool- and warm-season turfgrass since the 1990s. How - ever, reports of breakthrough, particularly from products containing the active ingredi - ent imidacloprid, have been surfacing in re- cent years on golf courses that have applied the active ingredient annually (and without rotation) for more than 10 years. We sought to determine whether site characteristics or enhanced soil microbial degradation could explain the lack of residual activity on af- fected sites. Five representative golf courses in New York and Pennsylvania were surveyed in 2017, and detailed spatial association analyses among grubs, turfgrass species and thatch lev - els were performed. Significant associations were detected between the spatial patterns of grubs and thatch at all sites. In all cases, grubs were more abundant in imidacloprid-treated roughs than in fairways. Ongoing greenhouse and field trials are aimed at identifying thatch ranges that impede imidacloprid uptake, as well as monitoring concentrations in differ - ent parts of the plant over time. Soils collected from roughs and fairways where imidaclo - prid was applied were assayed in greenhouse studies to determine the impact of microbial populations on the premature degradation of imidacloprid. Imidacloprid concentrations in perennial ryegrass grown in sterilized soils were significantly greater than those in the non-sterilized treatment between 14 and 56 days after treatment, indicating that microbial populations may also reduce efficacy. Ongo - ing studies are characterizing degradation under field conditions to determine whether these differences cause observable differences in white grub control. — Andrew Huling and Ben McGraw, Ph.D. (, Penn State Uni - versity, University Park, Pa. Teresa Carson ( is GCM 's science editor. Photo by Amy Duke Photo by Ron Townsend This research project was funded by a grant to GCSAA from the Environmental Instittute for Golf.

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