Carolina redroot (LAHTI) is a perennial weed of New Jersey cranberry beds. It is associated with “stand opening” areas that result from fairy ring dieback or other conditions of natural and anthropogenic origin. LAHTI accounts for significant yield reduction through direct competition with cranberry for nutritional resources. Field experiments were conducted from 2017 to 2022 on ‘Ben Lear’ and ‘Early Black’ cranberry beds in Chatsworth, NJ, to determine 1) the efficacy of residual herbicides labeled for use on cranberry, and subsequently, 2) to evaluate the value of overlapping preemergence applications of napropamide and postemergence applications of mesotrione for LAHTI control while minimizing crop phytotoxicity. Treatments in the first experiment included preemergence applications of dichlobenil or norflurazon at 2.2 and 4.5 kg ha–1 and napropamide a 6.7 kg ha–1. In the second trial, napropamide was applied preemergence annually to plots at 6.7 or 10.1 kg ha–1 either as a single or as two equally or unequally split applications spaced 30 d apart, followed by or not followed by mesotrione applied postemergence at 280 g ha–1 when LAHTI leaves emerged above the cranberry canopy. The preemergence herbicides dichlobenil applied at 4.5 kg ha–1 and napropamide provided ≥48% LAHTI control and ≥40% LAHTI biomass reduction 112 d after treatment (DAT), whereas norflurazon had no significant effect on LAHTI biomass. Less than 4% of crop injury and liquid formulation adapted to chemigation identified napropamide as an effective preemergence herbicide for LAHTI control. In the second trial, napropamide applied at 10.1 kg ha–1 followed by an application of mesotrione reduced LAHTI biomass by ≥73%. Splitting napropamide application reduced yield by 36% and berry weight by 12% compared with a single application at the dormant stage. Compared with the nontreated control, a single napropamide application at 10.1 kg ha–1 followed by an application of mesotrione increased yield by 38%. Information derived from these studies is already being used by growers to enhance the productivity and profitability of New Jersey cranberry fields.
Nomenclature: Dichlobenil; mesotrione; napropamide; norflurazon; Carolina redroot, Lachnanthes caroliniana (Lam.) Dandy LAHTI; large cranberry, Vaccinium macrocarpon Ait.
