Weed management options during seeded establishment of tall fescue [Schedonorus phoenix (Scop.) Holub; Lolium arundinaceum (Schreb.) S.J. Darbyshire] are limited. Siduron is often applied at planting for preemergence control of warm-season annual grasses such as crabgrass (Digitaria spp.) species (Moshier et al., 1976; Shearman et al., 1980). Siduron does not control annual broadleaf weeds and has little postemergence activity (Vencill, 2002). Quinclorac can be used both pre- and postemergence for control of crabgrass and some broadleaf species, but it does not control goosegrass [Eleusine indica (L.) Gaertn.] (Johnson, 1996; Reicher et al., 1999; Vencill, 2002; Zawierucha and Penner, 2001).
Mesotrione is currently being evaluated for use in turfgrass. Mesotrione inhibits p-hydroxyphenylpyruvate dioxygenase (EC 188.8.131.52), a precursor to plastoquinone and tocopherols (Mitchell et al., 2001; Pallett et al., 1998; Secor, 1994). The predominant symptom of mesotrione activity is tissue whitening with subsequent plant necrosis. Whitening is attributed to a decrease in carotenoid production resulting from decreased phtytoene desaturase activity. Mesotrione is an indirect inhibitor of phytoene desaturase because plastoquinone serves as a cofactor for phytoene desaturase, the first step in the carotenoid synthesis pathway converting phytoene to ζ-carotene and successive carotenoids. The lack of tocopherols also contributes to plant death through a decrease in buffering capacity to reactive oxygen species (Matringe et al., 2005).
Some turfgrass species have been reported to have tolerance to mesotrione. Mesotrione applied at 0.44 kg·ha−1 injured Kentucky bluegrass less than 25% 8 weeks after treatment and controlled crabgrass (Digitaria spp.) more than 80% 8 weeks after treatment (Beam et al., 2004). Sequential applications of mesotrione at 0.14 kg·ha−1 applied at seeding and 4 weeks after seeding (WAS) of tall fescue controlled crabgrass species more than 90% with tall fescue cover exceeding 90% 22 WAS (Askew et al., 2003). In comparison, tall fescue groundcover was 15% to 35% less than the nontreated at 22 WAS when treated with quinclorac applied at 0.84 kg·ha−1 at seeding or 0.84 kg·ha−1 at seeding followed by (fb) 0.42 kg·ha−1 4 WAS (Askew et al., 2003). Tall fescue has also been reported to be more tolerant than Kentucky bluegrass, red fescue, and perennial ryegrass to the p-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide isoxaflutole (Bhowmik and Drohen, 1998).
Mesotrione provides control of large crabgrass (Digitaria sanguinalis L.) (Johnson and Young, 2002), smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb ex. Muhl.], henbit (Lamium amplexicaule L.), broadleaf plantain (Plantago major L.), yellow woodsorrell (Oxalis stricta L.) (Askew et al., 2003), and nimblewill (Muhlenbergia schreberi J.F. Gmel.) (Willis et al., 2005). Based on these experiments, it was hypothesized that mesotrione could be used during seeded establishment of tall fescue with minimal reduction in grow-in speed. Experiments were conducted to evaluate seedling tall fescue tolerance and grow-in to mesotrione and quinclorac.
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