Roughstalk Bluegrass Control in Creeping Bentgrass with Bispyribac-sodium and Sulfosulfuron Patrick E. McCullough and Stephen E. Hart Rutgers, The State University of New Jersey Introduction Roughstalk bluegrass (Poa trivialis L.) is a problematic weed in creeping bentgrass that reduces turf aesthetics and functionality. Roughstalk bluegrass generally has a pale green color, coarser leaf texture, and has poor tolerances to disease, heat, and environmental stresses. Bispyribac-sodium and sulfosulfuron are selective herbicides for roughstalk bluegrass control but comprehensive investigations regarding rates and application regimens for long-term control are limited. Results and Discussion Roughstalk Bluegrass Control Roughstalk bluegrass cover of untreated plots declined by approximately 50% from June to August but was comparable to initial populations by fall and spring (Tables 1, 2, and 3). All bispyribac-sodium treatments reduced roughstalk bluegrass ground cover similarly, averaging 80 to 95% reductions, by August in all three years. Sequential sulfosulfuron applications were more effective than single treatments in 2005 but all regimens provided similar roughstalk bluegrass reductions in 2006 and 2007, ranging 80 to 95% of untreated. Despite substantial reductions in populations from herbicide treatments in summer, roughstalk bluegrass regrowth comparable to initial populations was noted in fall and spring of all three years (Picture 1a, b). Creeping Bentgrass Responses Creeping bentgrass chlorosis from herbicides was acceptable (< 20%) by three weeks after applications (data not shown). There were no meaningful differences detected in turf quality between treated and untreated plots (not shown). Table 1. Roughstalk bluegrass cover following herbicide treatments in field experiments, 2005-2006, Basking Ridge, NJ. Herbicides were applied June 10, July 1, and July 19 in 2005 and reapplied to the same plots on June 1, June 26, and July 27 in 2006. Sulfosulfuron treatments included a non-ionic surfactant at 0.25% v/v.   Roughstalk Bluegrass Cover Treatment Rate Applications 7/1/05 8/15/05 9/7/05 10/28/05 5/18/06 7/10/06 8/9/06 10/10/06 g ai/ha ----------------------------------------------------- % --------------------------------------------------- Bispyribac-sodium 37 2 22 ab 2 bc 3 bc 13 a 31 ab 5 b 2 b 11 b 3 12 ab 1 c 0 c 11a 24 ab 0 b 9 b 74 10 b 9a 18 b 4 b 1 b 18 ab 15 a 34 ab 3 b 15 ab 111 12 b Sulfosulfuron 12 2 c 8a 17 ab 13 b 20 ab 24 13 ab 18 a 41 a 19 ab 14 ab 33 ab 8 b 48 12 a 21 ab 1 8 ab 10a 23 ab 30 a Untreated 12a 25 ab 16 a Objective To investigate bispyribac-sodium and sulfosulfuron efficacy for roughstalk bluegrass control in creeping bentgrass fairways. Table 2. Roughstalk bluegrass cover following herbicide treatments in field experiments, 2006-2007, Basking Ridge, NJ. Herbicides were applied June 1, June 26, and July 27 in 2006 and reapplied to the same plots on May 30, June 25, and July 24 in 2007. Sulfosulfuron treatments included a non-ionic surfactant at 0.25% v/v. Materials and Methods Three field experiments were conducted on a creeping bentgrass fairway from June 2005 to October 2007 at New Jersey National Golf Course in Basking Ridge, NJ. The fairway was a creeping bentgrass blend of ‘Penncross’, ‘Southshore’, and ‘Seaside’ established in 1995 on a silty clay soil with a 6.8 pH. Turf was fertilized at 8 kg N/ha per month and was mowed three times per week at 8 mm with a reel-type mower. Initial roughstalk bluegrass populations were approximately 25% ground cover on days of initial applications. Experimental Design and Treatments. Experimental design was a randomized complete block with four replications of 1 x 3-m plots at all locations. Treatments were applied by making two passes per plot in opposite directions with a single nozzle CO2 pressured sprayer calibrated to deliver a total 375 L ha-1. Nozzles used were 9504E (Tee Jet®, Spraying Systems Co. Wheaton, IL 60189) and set for 220 kPa. Experiments 1 and 2 were initiated in June 2005 and 2006, respectively, and received herbicide applications on the same plots in 2006 and 2007, respectively. Experiment 3 was initiated in June 2007. Data Collection and Analysis. Leaf chlorosis was visually rated percent scale where 100 equaled dead grass and 0 equaled dark green grass. Turf quality was rated on a 1 to 9 scale where 1 equaled dead turf and 9 equaled ideal, uniform turf. Roughstalk bluegrass cover was visually rated on percent scale before initial applications and periodically throughout the experiment. Data were subjected to analysis of variance and means were separated with Fisher’s Protected LSD test at a = 0.05. Roughstalk Bluegrass Cover Treatment Rate Applications 7/10/06 8/9/06 10/10/06 5/30/07 7/11/07 8/7/07 9/25/07 g ai/ha ------------------------------------------- % ---------------------------------------- Bispyribac-sodium 37 2 2 b 0 b 7 ab 1 b 0 c 9 abc 3 3 b 4 ab 4 b 74 5 ab 10 ab 6 bc 9 ab 1 bc 111 6 b 11 a 5 c Sulfosulfuron 12 3a 8 abc 24 2 ab 11 ab 8 ab 48 11a 1 0 bc 10 abc Untreated 13 a 5a Conclusions Bispyribac-sodium and sulfosulfuron have potential to control roughstalk bluegrass in summer months but regrowth by fall and spring may limit potential for long-term success. Table 3. Roughstalk bluegrass cover following herbicide treatments in field experiments, 2007, Basking Ridge, NJ. Herbicides were applied May 30, June 25, and July 24 in 2007. Sulfosulfuron included a non-ionic surfactant at 0.25% v/v. Roughstalk Bluegrass Cover Treatment Rate Applications 7/11/06 8/7/06 9/25/06 g ai/ha ---------- ---------------------- % ------------------------------- Bispyribac-sodium 37 2 1 b 0 b 14 a 3 5 b 74 7 ab 9 ab 111 5 ab 11 ab Sulfosulfuron 12 3 b 10 ab 24 4 b 13 a 2 b 1 8 ab 48 Untreated 11 a 9a Picture 1. Roughstalk bluegrass reductions following herbicide treatments in August (a) and subsequent regrowth (b) in fall. a b