Susceptibility of American burnweed (Erechtities hieraciifolius) to herbicides and clipping in wild blueberry (Vaccinium angustifolium Ait.)

Abstract

American burnweed is an increasingly common annual weed in wild blueberry fields in Atlantic Canada. Knowledge of susceptibility to several common herbicides used in wild blueberry, however, is lacking, and it is unclear how burnweed responds to clipping. Using greenhouse-grown plants, the objectives of this research were to evaluate burnweed susceptibility to various herbicides registered in wild blueberry and to determine the effect of clipping on burnweed lateral branch and flower production. Postemergence broadcast applications of mesotrione, flumioxazin, glufosinate, clopyralid, foramsulfuron, glyphosate, tribenuron methyl, nicosulfuron/rimsulfuron, terbacil, and hexazinone provided >90% control of burnweed. Postemergence spot applications of clopyralid, glyphosate, mesotrione, and nicosulfuron/rimsulfuron to 24 ± 0.3 cm tall burnweed plants caused 60%–97% injury, but <50% of treated plants died. In contrast, spot applications of glufosinate, tribenuron methyl, and foramsulfuron provided complete control of treated plants. Efficacy of postemergence broadcast mesotrione and foramsulfuron applications declined with increasing burnweed plant height, although foramsulfuron provided greater control of plants >10 cm in height than mesotrione. A tank mixture of mesotrione and foramsulfuron was effective on burnweed and may be useful for controlling plants of varying size with broadcast applications in the field. Removal of 25%, 50%, and 75% of aboveground burnweed stems with clipping increased lateral branch numbers relative to untreated control plants, and 100% removal of the aboveground stem was required to prevent lateral branching and flowering. Stem removal through mowing under field conditions will likely have limited effects on burnweed, and herbicides are recommended for burnweed management in wild blueberry.