An Intercollegiate Approach to Quantifying Sulfonylurea Herbicide Movement Onto Cool-Season Turfgrass.

Sulfonlyurea (SU) herbicides are used in warm-season turfgrass for removal of cool-season grasses, including overseeded perennial ryegrass (Lolium perenne L.).  Research has indicated SU herbicides can remain on the treated leaf surface for several days following application increasing their potential to be tracked onto sensitive grasses, like creeping bentgrass (Agrostis stolonifera L.), via equipment tires.  Flazasulfuron is an SU herbicide currently labeled for use in commercial turfgrass systems.  Prior to its registration, the Environmental Protection Agency (EPA) required a 30-m buffer when applied near creeping bentgrass putting greens due to potential tracking injury via foot-traffic.  However, no research has quantified SU herbicide movement onto creeping bentgrass putting greens via foot-traffic.  Therefore, a collaborative approach between multiple universities was taken to quantify SU herbicide movement via foot-traffic onto creeping bentgrass putting greens.  Research was conducted in 2009 at Auburn University, Clemson University, North Carolina State University, University of Tennessee, and Virginia Tech.  Studies were arranged in 2 x 6 x 3 x 3 factorial in a randomized complete block split-split-split plot design: irrigation prior to tracking event (irrigated vs non-irrigated turfgrass) served as the whole plot factor while herbicide treatment (flazasulfuron at 9, 26, and 52 g ai ha^-1, trifloxysulfuron-sodium at 18 and 30 g ai ha^-1, and a nontreated check) served as the subplot factor; buffer distance (1.5, 4.6, and 7.6 m) served as the sub-subplot factor, while the sub-sub-subplot factor was tracking event (1, 2, and 3 days after treatment (DAT). Visual injury and normalized differential vegetation index (NDVI) ratings were made at each location. Statistically significant (P< 0.01) irrigation-by-buffer distance and irrigation-by-tracking event interactions were detected in visual injury and NDVI data when pooled across herbicide treatments.  However these interactions were not considered biologically significant as creeping bentgrass injury measured <1%.