Dollar Spot Severity and Oxalic Acid Production Affected By Nitrogen Fertilization in Creeping Bentgrass.

Dollar spot (caused by Sclerotinia homoeocarpa) is the most economically important disease of amenity turfgrasses grown in North America. Previous research has demonstrated that nitrogen fertilization may reduce dollar spot severity, however the results have been mixed and the impact of nitrogen on S. homoeocarpa’s production of the virulence factor oxalic acid is unclear. The objectives of this study were to evaluate nitrogen fertilization impacts on dollar spot severity in the field and how the production of oxalic acid is influenced by nitrogen and ambient pH in vitro. The three-year field trial was initiated in spring 2015 and tested the impact of 4 different nitrogen rates (4.88kgN/ha, 9.76kgN/ha,19.42kgN/ha, 29.29kgN/ha) on ‘Penncross’ creeping bentgrass maintained at putting green height at locations in Madison, WI and Glenview, IL. The in vitro assays measured oxalic acid production and pH change of two S. homoeocarpa isolates grown in potato dextrose broth (PDB) media. Results from the field trial indicated that the 29.29kgN/ha rate of nitrogen provided dollar spot suppression comparable to a fungicide program while all of the lower nitrogen rates were comparable to the non-treated control. In vitro results demonstrated that more oxalic acid was produced by the fungus when initial PDB pH was at 7 compared to an initial pH of 4. This research demonstrates that nitrogen fertilization alone can provide effective dollar spot suppression, and that the production of oxalic acid by the fungus may be to create a more favorable pH for fungal infection. Future techniques altering the production of oxalic acid through nitrogen fertilization and other cultural practices may lead to novel management strategies for this important disease.