Bermudagrass is the primary warm-season turfgrass species grown in the United States (Christians, 2011). Common to home lawns, athletic fields, and golf courses, bermudagrass is adapted to the southern and central regions of the transition zone (Christians, 2011). The abundant production of aggressive rhizomes and stolons enables bermudagrass to tolerate wear and recover from stress quicker than cool-season turf (Beard, 1973; Youngner, 1961). However, this may also make it a difficult to control weed in some turfgrass environments (Griffin et al., 1994; Johnson and Carrow, 1993). Creeping bentgrass is frequently used as a golf course putting surface in warm, temperate climates where bermudagrass is adapted to grow. Bermudagrass is capable of encroaching into putting greens from neighboring surrounds because optimum bermudagrass growth occurs from June through August when creeping bentgrass is often experiencing stress (Christians and Engelke, 1994; Turgeon, 2011). The presence of bermudagrass in creeping bentgrass greens can disrupt the playing surface and reduce aesthetic quality (Johnson and Carrow, 1993; Lowe et al., 2000).
Limited options exist for the selective control of bermudagrass in managed turfgrass. The use of siduron for the control or suppression of bermudagrass in creeping bentgrass putting greens has been inconsistent. McMaugh (1971) reported complete control of common bermudagrass in response to sequential applications of siduron at 40.11 lb/acre at 12-week intervals. Although ‘Tifdwarf’ hybrid bermudagrass (C. dactylon × Cynodon transvaalensis Burtt-Davy) growth was suppressed with sequential (4- to 6-week intervals) applications of siduron at 17.83 lb/acre, Duble (1974) suggested additional applications would be necessary to prevent further encroachment. Siviour and Schultz (1984) observed no change or increased common bermudagrass cover in response to single or sequential applications of siduron at 44.57 lb/acre. Johnson and Carrow (1993) reported that tank-mixing siduron with flurprimidol at 48.13 + 0.71 lb/acre in March followed by 12.48 + 0.18 lb/acre in April and May resulted in 83% to 94% bermudagrass suppression by mid-June. Single and sequential applications of ethofumesate (0.36 to 1.52 lb/acre) + flurprimidol (0.18 to 0.71 lb/acre) made from March until May exhibited 88% to 99% bermudagrass suppression by mid-June. Sequential applications of fenoxaprop at 0.06 lb/acre in April, May, and June resulted in 75% suppression of common bermudagrass by mid-June, but only 14% and 26% suppression of ‘Tifway’ and ‘Tifgreen’ hybrid bermudagrass, respectively (Johnson and Carrow, 1993). Doroh et al. (2011) observed similar control (32%) of ‘Tifway’ bermudagrass 9 WAIT following sequential applications of fenoxaprop at 0.09 lb/acre. Sequential treatments of fenoxaprop alone or in combination with triclopyr resulted in the lowest percent cover of common bermudagrass (3% to 19%) at the end of the growing season (Cudney et al., 1997).
Herbicide rates required for bermudagrass control often result in unacceptable levels of creeping bentgrass phytotoxicity. Johnson and Carrow (1993) observed 50% to 77% and 23% to 45% phytotoxicity on ‘Penncross’ creeping bentgrass 10 d after treatment (DAT) with fenoxaprop at 0.12 lb/acre and ethofumesate + flurprimidol at 1.52 + 0.71 lb/acre, respectively. Higgins et al. (1987) reported that fenoxaprop at 0.06 and 0.13 lb/acre did not reduce creeping bentgrass color ratings below 4.5, while fluazifop at 0.09, 0.18, and 0.27 lb/acre reduced creeping bentgrass color ratings below 2.9 14 DAT. Henry and Hart (2004) observed a 20% and 40% reduction in clipping weight 4 weeks after treatment (WAT) of ‘L-93’ creeping bentgrass in response to fenoxaprop at 0.06 and 0.13 lb/acre. Reductions in turfgrass quality not only affect creeping bentgrass aesthetic appearance but may also reduce its competition, making it more susceptible to invasion from other weeds [e.g., annual bluegrass (Poa annua L.)] (Johnson, 1984; Turner et al., 1979).
Metamifop is a postemergence aryloxyphenoxypropionic acid herbicide used for the control of a wide range of annual and perennial grass weeds in cereal crops and rice (Hae-Jin et al., 2002; Moon et al., 2007). Doroh et al. (2011) observed 36% ‘Tifway’ hybrid bermudagrass control 9 WAIT in response to sequential applications of metamifop at 0.36 lb/acre. Tank-mixing metamifop at 0.36 lb/acre with triclopyr at 1 lb/acre increased bermudagrass control to 93% at 9 WAIT (Doroh et al., 2011). Askew and Goddard (2010) and Alea et al. (2010) observed minimal turfgrass injury (≤ 10%) when metamifop was applied to creeping bentgrass at 0.36 lb/acre. Furthermore, Gomez de Barreda et al. (2013) reported that metamifop at 0.18 lb/acre applied 4 weeks after seeding (WAS) ‘Penn A-4’ creeping bentgrass did not reduce turfgrass cover. Metamifop could potentially be an alternative chemical control for the removal of bermudagrass in cool-season turf with little to no phytotoxicity. Therefore, the objective of our research was to evaluate the efficacy of metamifop for common bermudagrass control in a greenhouse environment.
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