ABSTRACT
Weed control is important in the development and long-term management of commercial stands of the native lowbush blueberry (Vaccinium angustifolium Ait.). Unlike most fruit crops, the principle weeds include a wide range of woody and herbaceous native species (Hall, 1959; Jensen, 1985). These weeds are mostly perennials that also survive and thrive under the two-year prune management system. Prior to the 1980s, weed control depended on cutting and roguing and on the limited use of several nonselective herbicides, e.g., 2,4-D and dicamba, that were applied as directed spot sprays or by roller/wiper applicators (Trevett, 1950). The introduction in the early 1980s of hexazinone, a selective, broad-spectrum and residual herbicide that was applied broadcast in newly-pruned blueberry fields, provided control of most of these native species (Jensen, 1985; Yarborough and Bhowmik, 1989). Improved weed control resulted in rapidly increasing yields. The repeated use of this single herbicide has since resulted in changes in the weed flora to species that, like the lowbush blueberry, are also tolerant to the herbicide, e.g., bunchberry and black chokeberry (see Table 1 for all common and Latin names). Some species have developed tolerant populations after repeated exposure (e.g., some native Agrostis and Festuca spp.), whereas others are injured but eventually recover from labeled rates (e.g., wild rose and black bulrush) or re-establish from seed after soil residues have dissipated (e.g., lamb’s quarters and some goldenrods) (authors’ unpublished data). These species often occur in patches
in hexazinone-treated blueberry fields and could best be controlled by spot or directed foliar applications of selective herbicides. Currently in Canada there are only nonselective herbicides approved for use in lowbush blueberry that can be used as foliar sprays, e.g., 2,4-D/dicamba mixtures, triclopyr, and glyphosate. These cause severe injury when the crop is contacted by spray or spray drift (Atlantic Committee on Fruit Crops, 1999). Hence, they are used primarily in early stages of field development. There is a need to find selective herbicides that can be used within producing fields to control escaping weed species. This article will describe the selective control of some important hexazonone-tolerant weed species with spot applications of two sulfonylurea herbicides.
