Objective:   Evaluate herbicide combinations for selective bermudagrass control in cool-season turf.

Rational:   Bermudagrass is an aggressive warm-season turfgrass that spreads by stolons, rhizomes, and seeds. Once bermudagrass is established in cool-season turf, it is difficult to control, and negatively impacts aesthetics of a cool-season lawn.  No selective control is available for common bermudagrass in cool-season turfgrass.   Acclaim^TM (fenoxaprop-P) and Turflon^TM (triclopyr) are labeled for bermudagrass suppression, however long term control varies and depends on many factors.   Recent work has concluded that sequential applications of mesotrione can selectively remove bentgrass and nimblewill from cool-season turfgrass, without injuring tall fescue, perennial ryegrass, or Kentucky bluegrass.   Previous efforts using mesotrione alone for bermudagrass control have been unsuccessful.   However, applications of mesotrione are very injurious to bermudagrass indicating potential for control.  

Procedures:   This ongoing trial was established spring 2005 on an overseeded Vamont bermudagrass fairway. The fairway had not been transitioned for two previous years so the bermudagrass base was similar to a natural infestation with 30% bermudagrass cover in early spring and 60-75% cover in late summer.   Treatments included Acclaim^TM, Turflon^TM, and mesotrione, alone and in all possible combinations, applied two or three times in both spring and fall for bermudagrass control.   The first spring treatment was applied at 60% greenup and successive applications were made at three week intervals.   Fall applications were applied 9, 6, and 3 weeks prior to expected senescence.   In spring of 2006 after complete bermudagrass greenup foramsulfuron (Revolver) and quinclorac (Drive) were used to control perennial ryegrass and crabgrass, this allowed bermudagrass to be more visible for plot evaluation proposes.  

Results:   For all herbicides and combinations, 6 applications significantly reduced bermudagrass cover more than 4 applications.   Perennial ryegrass injury from spring applications was not significant at any timing.   Treatments injured perennial ryegrass as much as 35%, however, injury was short lived, and turfgrass recovered by 3 weeks after application.   Applications of mesotrione produce extremely chlorotic bermudagrass, essentially turning bermudagrass white, significantly reducing color ratings.   Mesotrione plus Turflon^TM plus Acclaim^TM and mesotrione plus Turflon^TM does not have this characteristic effect on bermudagrass.   The three-way combination had higher turf color ratings than mesotrione alone.   Mesotrione was more effective for bermudagrass control than Acclaim^TM or Turflon^TM, and, when applied six times, reduced bermudagrass cover by 80% one year after treatments were completed.   The best performing treatments were Mesotrione plus Turflon^TM, Turflon^TM plus Acclaim^TM, and Mesotrione plus Turflon^TM plus Acclaim^TM, with 95, 91, and 98% bermudagrass cover reduction, respectively.    These treatments would be more economical and likely less injurious when spot applied instead of broadcast applied.   Continuing research includes optimization of application timings for these treatments and optimizing product rates for these combinations.