Sheep sorrel is an invasive, creeping perennial weed of lowbush blueberryfields. It is one of the most prominent weeds in blueberry fields in NovaScotia and is responsible for decreasing yields. Three levels of fertilizer(0, 20, 40 kg N ha−1) and two levels of hexazinone (0 or 1.92 kgai ha−1) were applied to experimental plots to determine theireffects on sheep sorrel density. Sprout-year hexazinone reduced sheep sorreldensities, which led to increased yields. Fertilizer increased weed densityin the absence of herbicides, had no effect on density in the presence ofherbicides, tended to have no impact on floral buds, and did not increaseyields. Fruiting-year hexazinone decreased sheep sorrel densities in somesituations, but did not result in yield increases.

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.