Annual bluegrass (Poa annua L.) is a problematic weed that reduces turfgrass aesthetics, functionality, and surface quality (Beard, 1970). Compared with most turfgrasses, annual bluegrass has a lighter green color, shallow root system, and produces unsightly seedheads (Lush, 1989; Sprague and Burton, 1937). Annual bluegrass tolerates close mowing, germinates rapidly, and has undesirable qualities, including poor disease, drought, and wear tolerance that can reduce turf quality (Beard et al., 1978; Kaminski and Dernoeden, 2007; Lush, 1989). Consequently, turf infested with annual bluegrass requires increased water, fungicides, and intensive management to maintain acceptable quality, especially in the summer months.
Annual bluegrass can be selectively controlled in creeping bentgrass (Agrostis stolonifera L.), perennial ryegrass (Lolium perenne L.), and tall fescue (Festuca arundinacea Schreb.) with an acetolactate synthase inhibitor, bispyribac-sodium (Lycan and Hart, 2005a, Lycan and Hart, 2006a; McCullough and Hart, 2009). Although highly active on annual bluegrass in warm weather (20 °C or higher), bispyribac-sodium efficacy is often reduced under cool temperatures (20 °C or less), which may limit application timings in spring (Lycan and Hart, 2006a; McCullough and Hart, 2006). Ethofumesate, mesotrione, and sulfosulfuron have activity on young annual bluegrass plants, but limitations of tolerant turf species, inconsistent efficacy, and required application regimes restrict the potential for these herbicides to be used for annual bluegrass control in cool-season turfgrasses (Hart and McCullough, 2009; Johnson et al., 1989; Lycan and Hart, 2005b, 2006a; Lycan et al., 2005).
Application timing of postemergence herbicides for annual bluegrass control has been reported to influence establishment of turfgrasses from seed. Lycan and Hart (2006b) noted reductions in creeping bentgrass, kentucky bluegrass (Poa pratensis L.), and perennial ryegrass seedling cover from bispyribac-sodium applied 1 week before seeding (WBS), but these grasses were safely established when herbicides were applied 2 WBS. Common bermudagrass (Cynodon dactylon L.) seedlings have shown significant injury and reduced establishment from rimsulfuron, simazine, and trifloxysulfuron applied 1 to 2 WBS (McCullough and Nutt, 2010; Willis et al., 2007). Furthermore, researchers noted sulfosulfuron at 13 to 26 g/a.i./ha applied the day of seeding or 1 WBS significantly reduced creeping bentgrass and kentucky bluegrass establishment from the untreated. Thus, reseeding intervals may be critical for new herbicides introduced for postemergence annual bluegrass control in turf management regimes.
Amicarbazone is a photosystem II-inhibiting herbicide used for broadleaf weed control in corn (Zea mays L.) and sugarcane (Saccharum officinarum L) production (Senseman, 2007). Amicarbazone has soil residual activity, but postemergence applications also control susceptible weeds (Senseman, 2007). Field experiments have noted that sequential amicarbazone applications in spring of 0.1 to 0.4 kg·ha−1 effectively controlled annual bluegrass without causing unacceptable injury (greater than 20%) to creeping bentgrass, kentucky bluegrass, perennial ryegrass, and tall fescue (McCullough et al., 2010; Yelverton, 2008). Amicarbazone may also have greater efficacy than acetolactate synthase inhibitors such as bispyribac-sodium when applied during cooler weather in late winter or early spring, which may provide new options to end-users for selective annual bluegrass control in cool-season turf (McCullough et al., 2010).
Turfgrass managers may need to reseed desirable turfgrasses into voids remaining after annual bluegrass has been eradicated by amicarbazone or other postemergence herbicides. However, the soil residual activity of amicarbazone may inhibit turfgrass seedling establishment. Therefore, the objective of this research was to determine reseeding intervals for tall fescue and perennial ryegrass after amicarbazone applications.
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