Repeated applications of Callisto and Devrinol on newly planted cranberry vines

Abstract: To evaluate the weed control provided by various combinations of preemergence applications of Devrinol (napropamide) and postemergence applications of Callisto (mesotrione) in newly planted and 1-yr-old cranberry vines, six 2-yr experiments were conducted during 2009-2012. Three sites were treated in the year of planting plus the subsequent year (called “new plantings”) and three sites were treated in their second year of growth plus the subsequent year (called “second-year plantings”). Ten treatments, delivered in 3,735 L ha-1 water, were administered each year: Devrinol at 3.36 kg ai ha-1 applied once, twice, thrice or once followed by (fb) one application of Callisto at 210 g ai ha-1; Devrinol at 5.04 kg ai ha-1applied once, twice or once fb one application of Callisto at 210 g ai ha-1; Callisto at 210 g ai ha-1 applied once or twice; and nontreated. At new planting sites, plots receiving treatments other than a single Devrinol application had less total weed biomass compared to nontreated plots. At second-year plantings, all herbicide-treated plots had less total weed biomass than nontreated plots; in addition, plots receiving Callisto-only treatments had less total weed biomass than Devrinol-only treatments. Correlation analysis indicated that monocot biomass production was the primary positive predictor for total weed biomass. Herbicides did not adversely affect cranberry biomass production but overall vine colonization was poor for four of the six sites indicating that other factors, including cultivar choice, planting method, and water management, may play a larger role in rapid cranberry vine colonization than the suppression of initial weed biomass. Given the complementary range of efficacy for Devrinol and Callisto, a combination PRE-POST herbicide program of a low rate of Devrinol fb Callisto may be the most cost-beneficial program in many instances. If cost is a limiting factor, applying a single application of Callisto to a new planting should be included as a component of cranberry bed establishment since this practice consistently resulted in significantly less initial weed biomass compared to areas left nontreated. (accepted for publication in Weed Technology 7/2017