In the transition zone and especially in the piedmont region of Virginia, cool-season grasses have been primarily used for sports turf due to poor winter survival of warm-season grasses. Until recently bermudagrass [Cynodon dactylon (L.) pers.] has not been an option in these areas. New seeded bermudagrass (SB) varieties have promise to replace cool-season turf in these areas. Improved bermudagrass cultivars such as ‘Riviera’ tolerate cold temperatures and have very desirable color and texture characteristics while maintaining good wear tolerance and outstanding wear recovery. The ability to reseed makes renovating damaged sports turf much easier than sprigging hybrid varieties. Previous studies have evaluated the use of various chemicals on sprigged bermudagrass establishment. Few studies provide herbicide options for control of troublesome weeds during SB establishment. This field study was conducted to evaluate ‘Riviera’ SB response to carfentrazone, quinclorac and trifloxysulfuron applied to seedling SB.

The study was conducted on a fairway at the Virginia Tech Golf Course in Blacksburg, VA. Existing Kentucky bluegrass (Poa pratensis L.) was controlled with multiple applications of glyphosate and land was prepared by core aerating and vertical mowing each in two directions. Riveria SB was sown on June 4, 2004 at 48.8 kg pure live seed/ha and treatments were applied at various timings thereafter. The experimental design was a randomized complete block with 4 replications. Treatments included a nontreated check, carfentrazone at 0.03 kg ai/ha, carfentrazone plus quinclorac at 0.84 kg ai/ha, carfentrazone plus trifloxysulfuron at 0.03 kg ai/ha, and trifloxysulfuron at 0.03 kg ai/ha. Treatments were arranged in a factorial design with the aforementioned herbicides applied each at three timings relative to SB emergence [7, 14, and 24 day after emergence (DAE)]. SB emergence was noted on June 21 and treatments were made on June 28, July 05 and July 19.

Large crabgrass [Digitaria sanguinalis (L.) Scop.] control ratings were highly variable due to poor population. Treatments containing quinclorac and trifloxysulfuron applied before 14 DAE controlled large crabgrass greater than 70% 5 weeks after initial treatment (WAIT). Treatments that included trifloxysulfuron injured SB more than quinclorac or carfentrazone and trifloxysulfuron applications made at or before 14 DAE injured SB most. Trifloxysulfuron treatments injured SB greater than 50% 5 WAIT. This injury caused a 25% reduction in SB cover 11 WAIT. Quinclorac controlled large crabgrass without injuring SB. Trifloxysulfuron also controlled large crabgrass but caused unacceptable SB injury. To avoid SB injury trifloxysulfuron should not be applied until at least 28 DAE. When applied to young SB in any combination, carfentrazone and quinclorac did not cause injury at any timing.