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Evaluation of Acetic Acid for Weed Control in Organic Cranberry (Vaccinium macrocarpon Ait.) Production

Abstract: Trials were initiated in Tracy, NB and St. Louis de Kent, NB to evaluate the effectiveness of acetic acid on the control of weeds in organic cranberry production. Based on research conducted in Quebec, two application methods, injection and foliar, were evaluated under New Brunswick conditions. Injection evaluations involved the selection of four representative weeds of the same species where each weed in the set would be flagged and injected with a distinct concentration of acetic acid (2%, 6%, 12% and an untreated control). Multiple areas were selected and allowed testing over a broad range of weed species and were rated at various times over the season. Concurrently, plot research was conducted evaluating the four concentrations, listed above, injected into weed species within a one square metre plot area, replicated three times. An additional foliar experiment was initiated in Tracy to evaluate the effect of 0 %, 2% and 6% acetic acid applied until run-off. Visual evaluations of weed control and crop injury were made throughout the season, with crop yield measured at maturity. The application timings were later than the recommended timings due to late product delivery. As a result, observed crop injury levels may have been increased and weed control may be decreased in comparison to the optimal application timing. Injections of 12 % acetic acid caused limited crop injury, but this treatment was the only one to consistently offer a commercially acceptable level of weed control (greater than 80%). The 6 % level may offer a compromise between weed control and crop injury, although this level did not achieve control but only suppressed most weed species consistently. A 6 % foliar application was needed for adequate weed control, although this control was achieved though a reduction in cranberry tolerance. A 2 % foliar treatment offered some weed control and better crop tolerance, although this control was not complete and may not be acceptable to producers. Earlier application timings should be explored as cranberry tolerance would be greater earlier in the season, when weed tolerance may be lower.