2019 ASHS Annual Conference

Northern Highbush Blueberries (Vaccinium corymbosum) are an economically important crop for Oregon and the Pacific Northwest. Many organic growers apply synthetic mulches in the planting row and hand-weed to manage weeds in fields. As the cost of hand-weeding increases, alternatives are required. The object of this study was to compare the efficacy of saturated-steam (SW-900), brush-weeding (ID-brush weeder), ammonium nonanoate (AXXE®), and capric+ caprylic acid (Suppress®) to an untreated control. The experimental design was a five by five factorial arranged in a complete block with four replicates. Treatments were followed by a second application 28 days later resulting in all possible combinations (25 treatments). Sharp-point fluvellin (Kikxia elatine) and prostrate knotweed (Polygonum aviculare) were the most abundant weeds in the study. No significant interactions among sequential treatments were observed. At 28 DAT, total weed biomass was significantly reduced by saturated steam, brush weed, and ammonium nonanoate. A significant interaction among treatments was observed at the final evaluation. All treatments that included saturated-steam resulted in excellent total weed control (83-93%) regardless of the initial treatment. Performance of brush-weeder (58-89%), ammonium nonanoate (48-81%), and capric + caprylic acid (45-75%) were superior after a successful initial treatment, indicating that these treatments perform better against smaller weeds. Saturated-steam (88-95%) was the most consistently effective at controlling knotweed. Brush-weeding (65-94%), ammonium nonanoate (43-90%), and capric + caprylic acid (45-74%), although effective, were again dependent on the success of the initial treatment. Control of sharp-point fluvellin with saturated-steam (75-91%), brush-weeding (43-81%), ammonium nonanoate, (40-80%) and capric+ caprylic acid(42-55%) were effective but to a lesser degree than for total weed and knotweed control. At $32 and $42 per application per treated acre, respectively, saturated-steam and the brush-weeder were the most cost-effective tools. Ammonium nonanoate and capric + caprylic acid, cost $270 and $187 per treated acre, respectively. Saturated steam and brush-weeder are cost-effective weed control alternatives. These are early data from a study that continues until 2020.