Biannual applications of hexazinone have been applied in many lowbush blueberry fields in Nova Scotia for more than 30 years. Persistent reliance on a single herbicide chemistry may have selected for hexazinone-resistant red sorrel. The recommended rate of hexazinone (1.92 kg ai ha−1) no longer controls red sorrel in many growing regions. Six levels of hexazinone (0, 0.48, 0.96, 1.92, 3.84, and 7.68 kg ai ha−1) were applied to red sorrel plants grown in a greenhouse from seeds collected from three commercial fields and a no blueberry area to determine if they were hexazinone resistant. Red sorrel from two sites where hexazinone had not been applied regularly died at the 0.96 kg ai ha−1 rate of hexazinone whereas red sorrel from two commercial fields survived at 7.68 kg ai ha−1. It is concluded that red sorrel is hexazinone-resistant in some wild blueberry fields. A portion of the psbA gene was sequenced and it was determined that resistant plants had a Phe to Val substitution at position 255 in the D1 protein. This is the first recorded instance of hexazinone resistance in a perennial broadleaf weed in blueberry fields.
Nomenclature: Hexazinone, Velpar; red sorrel, Rumex acetosella L.; lowbush blueberry, Vaccinium angustifolium Ait.