Bermudagrass (Cynodon dactylon L.) is an aggressive and persistent weed that is difficult to control and decreases turf aesthetics. Fenoxaprop and triclopyr are used for bermudagrass suppression, however long term control is unreliable. Sequential applications of mesotrione control nimblewill (Muhlenbergia schreberi L.) in cool-season turfgrass and may be effective toward bermudagrass. Three trials were initiated in 2005 and 2006 in Blacksburg, VA to evaluate herbicide combinations for selective bermudagrass control in cool-season turf.

Research sites consisted of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) turf maintained as a golf course fairway naturally infested with common bermudagrass. Treatments were arranged in a factorial with two application scenarios and seven herbicide treatments, and experimental design was RCB with 3 replications. The two application scenarios were herbicide treatment, either two or three times in both spring and fall. The first spring treatment was applied at 60% bermudagrass greenup and successive applications were made at three-week intervals. Fall applications were applied 9, 6, and 3 weeks prior to expected senescence. The seven herbicide treatments were all possible combinations of fenoxaprop-P, triclopyr, and mesotrione at 246, 1123, and 140 g ai/ha, respectively, with a nontreated comparison.

For all herbicides and combinations, three applications significantly reduced bermudagrass cover more than two applications. When applied alone none of the herbicides controlled common bermudagrass greater than 65% one year after treatment (YAT). Treatments reducing common bermudagrass cover below 10% one YAT were viewed acceptable. Acceptable treatments were mesotrione plus triclopyr, triclopyr plus fenoxaprop-P, and mesotrione plus triclopyr plus fenoxaprop-P, with 9, 5, and 2% bermudagrass cover 1 YAT, respectively. In stressful conditions these treatments injured perennial ryegrass as much as 35%, however, injury was short lived, and turfgrass recovered by 3 weeks after application.