Creeping bentgrass (CBG) is a common weed in home lawns and golf course roughs and green surrounds in many regions of the United States. CBG is extremely competitive because of its stoloniferous growth habit. Once lawns, roughs, green surrounds, and other turfgrass areas are invaded by CBG, it can rapidly dominate the stand (Branham et al., 2005). Currently, no herbicides are registered that are known to safely and effectively remove CBG from desirable cool-season turfgrasses. The most widely used methods of removing CBG from cool-season turfgrasses include physical removal or the use of a nonselective herbicide. The use of a nonselective herbicide is undesirable in many situations because they may not completely eliminate the CBG in a single application, and large areas would require overseeding (Branham et al., 2005). In an unpublished Maryland study, however, four summer applications of the ester formulation of triclopyr applied at 1.12 kg·ha−1 a.i. were shown to safely control CBG in tall fescue (P.H. Dernoeden, unpublished data). Triclopyr ester is labeled for the control of selected broadleaf weeds, suppression of bermuda- grass (Cynodon spp.), and control of kikuyu grass (Pennisetum clandestinum Hochst. ex Chiov.; Dow AgroSciences, Indianapolis). Mesotrione is a herbicide that is labeled for use in corn (Zea mays L.) and was reported to be phytotoxic to CBG (Askew et al., 2003; Bhowmik and Riego, 2003; Syngenta Crop Protection, Greensboro, NC). More recently, researchers have reported on the use of mesotrione to selectively control CBG in Kentucky bluegrass (Beam et al., 2006; Branham et al., 2005; Jones and Christians, 2005). In the first year of a 2-year Illinois study, Branham et al. (2005) reported that two or three applications of mesotrione at 0.28 or 0.42 kg·ha−1 a.i. beginning in early June provided inconsistent levels (13%–92%) of CBG control. The 0.42 kg·ha−1 a.i. rate applied three times, however, provided 92% to 100% CBG control in both years. The generally poor level of CBG control observed in the first year may have been because of cooler temperatures at the time treatments initially were applied. In the second year, however, the aforementioned mesotrione treatments provided between 91% and 100% CBG control. They observed only short-lived discoloration in Kentucky bluegrass, which recovered in about 2 weeks after treatment. Jones and Christians (2005) reported that two applications of mesotrione at 0.70 and 1.12 kg·ha−1 a.i. in Iowa provided 38% and 99% CBG control in Kentucky bluegrass, respectively. In Virginia, Beam et al. (2006) applied mesotrione twice at 0.28 kg·ha−1 a.i. or three times at 0.06 and 0.17 kg·ha−1 a.i. beginning in September. All mesotrione treatments provided ≥92% CBG control in both study years while causing some short-lived injury to Kentucky bluegrass. Mesotrione also has herbicidal activity on several other common turfgrass weeds, including crabgrass (Digitaria spp.), nimblewill (Muhlenbergia schreberi J.F. Gmel.), white clover (Trifolium repens L.), and yellow nutsedge (Cyperus esculentus L.; Askew et al., 2003; Dernoeden et al., 2007; Keese et al., 2005). Some turfgrass managers may prefer to apply this herbicide in the summer to control a broader spectrum of weeds.
Triclopyr ester has received only limited study for the purpose of selective CBG control, and it merits further study. Although mesotrione has been shown to be effective, additional regional studies also are warranted to confirm or identify the most effective rate(s) and application frequency for selective CBG control. The aforementioned mesotrione studies were conducted in Kentucky bluegrass and perennial ryegrass (Lolium perenne L.). In the mid-Atlantic region, however, tall fescue has become the preferred species to use on home lawns and is gaining wide acceptance for use in golf course rough's and green surrounds (Bevard, 2007). The objectives of this study were to compare and fine tune mesotrione and triclopyr ester rates and summer application frequencies for the purpose of selective CBG control in tall fescue and Kentucky bluegrass. This field study was conducted in Connecticut and Maryland.
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