Field assessment of flazasulfuron and trifloxysulfuron sodium drift

Abstract

Exposure of non-target species pesticide via drift is of concern to the United States Environmental Protection Agency (EPA) as evidenced by required buffer zones and language on labels regarding offsite exposure to endangered species. In 2008, flazasulfuron received a conditional registration that specified a 30-m nontreated buffer between treated areas and sensitive plants. This buffer would make most intended uses of flazasulfuron in warm-season turfgrass impossible. Assessment of drift in field conditions is required to replace model-predicted buffer restrictions. Studies were conducted to assess drift of flazasulfuron and a similar herbicide, trifloxysulfuron sodium, in field conditions using conventional turfgrass spray equipment and maximum boom height and minimum droplet size specified on product labels. Herbicides were applied perpendicular to a 6.4 to 9.7 km h −1 wind over 'Riviera' bermudagrass [Cynodon dactylon (L.) Pers.] turf and sentinel corn plants were placed at distances between 0 and 30.5 m downwind. A bioassay based on reduction of corn height growth rate and shoot biomass indicated trifloxysulfuron sodium and flazasulfuron reduced corn growth similarly but the magnitude of these effects were dependent on year. Year dependency was likely associated with differences in corn cultivars between years. Herbicide drift was not detected beyond 4.6 m downwind of any application. Upon reviewing these and other data, EPA approved a label modification for flazasulfuron that reduced the minimum buffer to 7.6 m.

Turfgrass response to flazasulfuron and trifloxysulfuron sodium deposited by runoff water

“…Flazasulfuron at 9 g ha –1 injured L. perenne to a distance of 6 and 1 m below treated plots at FCC and TRC, respectively, and equivalent to trifloxysulfuron sodium (Table 2). In similar studies, trifloxysulfuron sodium at 16 g ha –1 injured L. perenne at distances equivalent to that observed for metsulfuron and rimsulfuron but less than that observed for pronamide (Askew & Murphy, 2009).…”

“…Pronamide at 1120 g ha –1 reduced L. perenne cover 88% at 0 to 60 cm downslope of treated plots in Florida (Leon et al., 2016), which is comparable to results at FCC (Table 1). When applied at 560 g ha –1 , pronamide injured L. perenne between 50 and 90% depending on location at 0 to 1 m downslope of treated plots in Georgia and Virginia (Askew & Murphy, 2009). Trifloxysulfuron sodium applied at 16 g ha –1 injured L. perenne between 3 and 83% and inconsistently between locations in Georgia and Virginia (Askew & Murphy, 2009).…”

“…When applied at 560 g ha –1 , pronamide injured L. perenne between 50 and 90% depending on location at 0 to 1 m downslope of treated plots in Georgia and Virginia (Askew & Murphy, 2009). Trifloxysulfuron sodium applied at 16 g ha –1 injured L. perenne between 3 and 83% and inconsistently between locations in Georgia and Virginia (Askew & Murphy, 2009). It should be noted that the severity of herbicide injury does not necessarily indicate the likeliness of herbicides to move or to cause injury symptoms in neighboring grasses.…”

“…ha –1 . Each plot was oriented such that sideward slope was less than 1% and downslope was between 7 and 11% as in other work (Askew & Murphy, 2009; Leon et al., 2016). At application, gravimetric soil water content was between 19 and 24% at Blacksburg, VA and between 28 and 38% at Charlottesville, VA.…”

“…Flazasulfuron and trifloxysulfuron sodium have at least 140‐fold higher water solubility and 200‐fold lower K oc (Senseman, 2007) than pronamide, thus indicating potentially greater mobility. Trifloxysulfuron sodium mobility in runoff water has been observed in Gossypium hirsutum L. (cotton) (Matocha et al., 2006a) and turfgrass (Askew & Murphy, 2009). Flazasulfuron mobility has not been reported.…”