Creeping bentgrass (Agrostis stolonifera L.) is a cool-season grass well adapted to golf course greens, tees, and fairways that forms a dense, smooth surface ideal for golf when maintained at mowing heights less than 1.25 cm. However, creeping bentgrass is competitive with other cool-season turfgrasses at higher mowing heights (7.5 to 10 cm) and often spreads into surrounding areas of Kentucky bluegrass (Poa pratensis L.) (Davis, 1958). Creeping bentgrass is considered a weed in these situations because it disrupts turfgrass uniformity (Beard, 1973). Perennial grasses are often the most difficult weeds to control because they possess characteristics similar to the desired turf species (Christians, 2004). Cultural weed management practices are ineffective and herbicides currently labeled to control creeping bentgrass are nonselective (Dernoeden, 1999).
Sulfosulfuron is a sulfonylurea herbicide that provides selective control of annual and perennial grassy and broadleaf weeds in wheat (Triticum aestivum L.; Maverick, 75% a.i.; Monsanto Co., St. Louis), noncrop areas (Outrider, 75% a.i.; Monsanto Co.), and in highly managed turfgrass areas (Certainty, 75% a.i.; Monsanto Co.). The herbicide inhibits the acetolactate synthase enzyme, which aids in the synthesis of the branch chain amino acids leucine, isoleucine, and valine (Schloss, 1995). A number of sulfonylurea herbicides have shown selective herbicidal activity against grassy weeds in grass crops (Bruce and Kells, 1997; Larocque and Christians, 1985; Maloy and Christians, 1986; Rabaey and Harvey, 1997).
Recent studies demonstrate that sulfosulfuron exhibits herbicidal activity on annual bluegrass (Poa annua L.) (Lycan and Hart, 2002; Taylor et al., 2002) and tall fescue (Festuca arundinacea Schreb.) (Lycan and Hart, 2004), but Kentucky bluegrass and perennial ryegrass (Lolium perenne L.) are tolerant of the herbicide at low application rates (Lycan and Hart, 2004). Although these reports reveal the differential responses of cool-season grasses to sulfosulfuron, its activity on creeping bentgrass is not understood at this time. In addition, the efficacy of herbicides is often dependent on environmental conditions and target species (Malefyt and Quakenbush, 1991; Miller et al., 1978; Nalewaja and Woznica, 1985). Therefore, the objectives of this study were to determine 1) the effect of sulfosulfuron rate and application date on control of creeping bentgrass, and 2) the effect of sulfosulfuron applications on Kentucky bluegrass safety.
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