Occurrence of hexazinone-resistant red sorrel (Rumex acetosella L.) and evaluation of spring non-bearing year and autumn bearing year herbicides for red sorrel management in lowbush blueberry (Vaccinium angustifolium Ait.) fields in Nova Scotia

Abstract

Weeds are a major limiting factor in wild blueberry production and compete with wild blueberries for space, light, moisture, and nutrients. Red sorrel is a common creeping herbaceous perennial weed in commercially managed wild blueberry fields in Nova Scotia, Canada. Herbicides are the primary source of weed control in wild blueberry fields and current management practices do not provide adequate control of red sorrel. Multiple experiments were conducted over two years to evaluate 1) ocurrence of hexazinone-resistant red sorrel 2) spring herbicide applications 3) autumn herbicide applications and 4) autumn mowing and application timing on herbicide efficacy on red sorrel in wild blueberry fields. The majority of red sorrel populations sampled from blueberry fields in Nova Scotia were susceptible to hexazinone despite the occurrence of resistant biotypes of this weed species. Autumn applications of dicamba, dichlobenil, and tribenuron-methyl gave most consistent reductions in over-wintered ramet density across sites and are tentatively recommended for red sorrel management in wild blueberry fields. Spring applications were less effective than autumn applications, though pyroxsulam, hexazinone + pyroxsulam, sulfentrazone and hexazinone + sulfentrazone significantly reduced total non-bearing year ramet density relative to the nontreated control. Efficacy of autumn herbicide applications on red sorrel was not affected by mowing or application timing. Results indicate that red sorrel will be most effectively managed by autumn herbicide applications in wild blueberry. Additional research is required to determine acceptable spring herbicide treatments for this weed species and also alternative treatments to control red sorrel in wild blueberry fields.