219 International Turfgrass Society Research Journal Volume 11, 2009 SAFETY OF BISPYRIBAC-SODIUM ON COLONIAL BENTGRASS AND INFLUENCE ON BROWN PATCH SEVERITY John E. Kaminski* and Alex I. Putman ABSTRACT Bispyribac-sodium can be used to selectively control ABG in stands of perennial ryegrass and creeping bentgrass. However, its safety is unknown when applied to CoBG, which can be found on golf course fairways in the Northeastern United States and other parts of the world. The primary objectives of this field study were to determine if the chlorosis elicited by BPS could be masked by tank-mixing the herbicide with a chelated iron (Fe) plus nitrogen (N) product and determine the effect of the herbicide on brown patch. Bispyribac-sodium was applied to mature, fairway-height CoBG two or three times at 49 or 74 g ai/ha on a two week interval. In 2005, BPS caused significant injury to ‘SR7100’ CoBG, but BPS+Fe+N did provide some respite from chlorosis. When applied to ‘Allister’ CoBG in 2007, BPS injury was less pronounced and BPS+Fe+N continued to provide near complete masking of chlorosis. In both years, BPS caused moderate to severe increases in brown patch, regardless of rate. Plots receiving two applications of BPS or BPS+Fe+N resulted in the least amount of brown patch when compared to other treated plots and had higher disease levels than the untreated control on the 2 or 3 to 4 rating dates, respectively. Plots receiving three applications of BPS or BPS and Fe+N generally had significantly greater percent brown patch on 4 of 5 rating dates when compared to the untreated control. Based on the results of this study, BPS may cause unacceptable injury to certain cultivars of CoBG, and is likely to increase brown patch severity. John E. Kaminski*, Assistant Professor, Department of Crop and Soil Sciences, The Pennsylvania State University, University Park, PA 16802, and Alex I. Putman, Former Graduate Student, Department of Plant Science, University of Connecticut, Storrs, CT, 06269. *Corresponding author: (john.kaminski@psu.edu).