Smooth crabgrass and goosegrass are problematic weeds in creeping bentgrass in the transition zone, an area that rests between the southern United States where warm-season grasses dominate, and the northern United States where cool-season grasses thrive. These weeds are able to survive low mowing heights, especially among cool-season grasses (Busey, 2003; Callahan, 1986). As herbicide-resistant populations of smooth crabgrass (e.g., quinclorac) and goosegrass (e.g., prodiamine and pendimethalin) increase and as cultural control methods can be ineffective in cool-season grasses, new herbicides will be needed to ensure future control (Busey, 2003; Callahan, 1986; Hart et al., 2004; Heap, 2015; Mudge et al., 1984).
Several herbicides have been registered for smooth crabgrass and goosegrass control in cool-season turfgrass (King, 1990; Parker et al., 1985). Fenoxaprop controls both crabgrass and goosegrass; however, past research has shown fenoxaprop to cause stunting and stand reduction in seedling tall fescue (Schedonorus arundinaceus), perennial ryegrass (Lolium perenne), and creeping bentgrass (Cudney et al., 1997; Dernoeden, 1987; Neal et al., 1990). Herbicidal control options of smooth crabgrass and goosegrass in creeping bentgrass also include quinclorac, siduron, and bensulide. However, previous research has shown stunting, thinning, or foliar phytotoxicity to both mature and immature cool-season turfgrasses including creeping bentgrass with varying rates and application timings of many of these herbicides as well (Busey, 2003; Cudney et al., 1997; Dernoeden, 1987; Mueller-Warrant, 1990; Neal et al., 1990; Warren et al., 1989). Currently, only bensulide and oxadiazon are explicitly registered for preemergence (PRE) smooth crabgrass and goosegrass control on creeping bentgrass putting greens (PBI/Gordon Corp., 2009; Quali-Pro, 2013). Given these limited options for controlling grass weeds in creeping bentgrass, new herbicidal control options would be beneficial for sustainable management.
Metamifop is an arloxyphenoxypropionate (AOPP) herbicide that has reported herbicidal activity on smooth crabgrass and goosegrass with safety to creeping bentgrass. Metamifop is not currently registered in the United States, but is used for POST annual and perennial weed control in Asia and the Middle East. It is used in many turfgrass systems including parks, golf courses, and gardens (Flessner and McElroy, 2011; Hoyle et al., 2012; Kim et al., 2003a, 2003b; Post and Askew, 2010). It is also used in many cereal crops such as rice (Oryza sativa) for control of annual and perennial grass weeds at 100 to 200 g·ha−1 (Moon et al., 2007, 2010). Along with smooth crabgrass and goosegrass, metamifop has also controls over annual grass weeds such as barnyardgrass (Echinochloa crus-galli), while remaining less injurious to cool-season grasses (Flessner and McElroy, 2011; Kim et al., 2003b; Post and Askew, 2010). Post and Askew (2010) observed that metamifop at 300 g·ha−1 controlled smooth crabgrass while causing <10% creeping bentgrass injury whereas comparable smooth crabgrass control with fenoxaprop completely killed creeping bentgrass putting greens.
Metamifop inhibits acetyl-CoA carboxylase (ACCase), the enzyme that catalyzes the first step in fatty acid synthesis for membranes and cell growth (Burton et al., 1987; Devine et al., 1993; Focke and Lichtenthaler, 1987; Senseman, 2007). Like other AOPP herbicides, metamifop does not affect eudicotyledonous plants because of limited activity against cytosolic, the prokaryotic ACCase (Burton et al., 1987; Senseman, 2007). It has been hypothesized that these differing activities of AOPP herbicides in cool-season grasses and the selectivity observed among grasses may be because of an altered binding site within the ACCase target enzyme (Senseman, 2007; Stoltenberg et al., 1989). Irrespective of the specific mechanism, metamifop appears to be safer to cool-season turfgrasses while offering comparable control to other herbicides currently marked for crabgrass and goosegrass control (Cox and Askew, 2014; Flessner and McElroy, 2011; Kim et al., 2003a; Post and Askew, 2010).
The most efficacious rates and sequential application timings to achieve smooth crabgrass and goosegrass control have not been established. In addition, creeping bentgrass tolerance to metamifop at different mowing heights must be assessed. Research was conducted to evaluate metamifop rates and sequential application timings for smooth crabgrass and goosegrass control compared with an industry standard, fenoxaprop. The second objective was to evaluate creeping bentgrass injury associated with varying rates and application timings of metamifop at two mowing heights.
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