Lowbush blueberry (V. angustifolium) is an economically important fruit crop in Canada that contributed $47.4 million CAD to farm gate value in 2017 (Agriculture and Agri-Food Canada, 2019). The plant is a rhizomatous perennial shrub (Hall et al., 1979; Pritts and Hancock, 1984) and commercial fields are developed from natural stands (Agriculture and Agri-Food Canada, 2019) that are managed under a 2-year production cycle. Plants are pruned to ground level by flail mowing in the first year (nonbearing year) to promote vegetative growth and emergence of new shoots from the rhizomes and emerged shoots flower and produce berries in the second year (bearing year) (Eaton et al., 2004; Wood, 2004). Weed management is difficult because of lack of tillage and crop rotation and the weed flora is dominated by woody and herbaceous perennial weeds (McCully et al., 1991), including several species of perennial grasses (Agriculture and Agri-Food Canada, 2019; Jensen and Yarborough, 2004).
Hair fescue (Festuca filiformis) is a common, tufted perennial grass in lowbush blueberry fields. Tufts form dense, competitive sods that can reduce lowbush blueberry yield by >50% (White, 2019; Zhang, 2017; Zhang et al., 2018). Many growers are also unable to harvest fields with hair fescue infestations due to inability of mechanical harvesters to move through dense tufts. Hair fescue is not controlled by preemergence nonbearing year hexazinone applications (White, 2019) and efficacy of preemergence nonbearing year terbacil applications is variable and limited primarily to suppression (White, 2019; Zhang et al., 2018). Postemergence foramsulfuron applications were recently registered for nonbearing year hair fescue suppression in lowbush blueberry and reduce flowering tuft density, flowering tuft inflorescence number, and flowering tuft seed production and seed viability (White and Kumar, 2017). However, efficacy is variable across sites and large tufts common in lowbush blueberry fields are not killed (Zhang et al., 2018). There is, therefore, interest from growers to use foramsulfuron as a sequential application in conjunction with other fall- or spring-applied herbicides, as this may improve hair fescue suppression (White and Kumar, 2017; White, 2019) and diversify the herbicide modes of action used to manage this weed species.
Herbicides currently registered for fall-bearing year applications in lowbush blueberry and that also have known or potential efficacy on hair fescue are limited to pronamide, dichlobenil, glufosinate, and terbacil. Pronamide is effective (White, 2019) and is considered the industry standard treatment for hair fescue. Dichlobenil is not widely used in lowbush blueberry due to high cost of broadcast applications (>$1400 CAD/ha), but suppressed red fescue (Festuca rubra) in lowbush blueberry (Sikoryia, 2014) and could provide an important alternative herbicide mode of action for hair fescue if effective. Fall-bearing year glufosinate applications alone do not control hair fescue but can reduce flowering tuft density and may increase suppression when followed by spring-nonbearing year foramsulfuron applications (White, 2019). This glufosinate use pattern, however, has not been widely evaluated. Fall-bearing year terbacil applications are registered for use in lowbush blueberry (New Brunswick Department of Agriculture, Aquaculture, and Fisheries, 2017) but are rarely used because previous research indicated lower weed control from fall relative to spring applications (Jensen, 1985a, 1985b). Fall-bearing year applications have not, however, been evaluated on a perennial grass such as hair fescue.
The objective of this research was to determine the main and interactive effects of fall-bearing year pronamide, dichlobenil, glufosinate, and terbacil applications and spring-nonbearing year foramsulfuron applications on hair fescue in lowbush blueberry fields.
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