Impact of Acetic Acid Concentration, Application Volume, and Adjuvants on Weed Control Efficacy

Acetic acid (CH3COOH) is produced naturally through anaerobic fermentation (vinegar) or synthesized through various industrial chemical methods. The primary components of vinegar are water and acetic acid. Acetic acid can destroy cell membranes, which then can result in plant tissue desiccation and plant death. Therefore, vinegar has the potential as a natural contact herbicide for the control of weeds in organically produced crops. Additional information is needed to determine the influence of acetic acid concentration, application volume, and adjuvants on weed control. Typically, household vinegar contains 5% acetic acid and greater acetic acid concentrations are available commercially. Field research was conducted in southeast Oklahoma (Lane, OK) to determine the effect of acetic acid concentrations, application volumes, and adjuvants on weed control efficacy. The factorial experimental design included three acetic acid concentrations (0, 5 and 20%), two sprayer application volumes (187 and 935 L/ha), three adjuvants (none, orange oil, and canola oil), and one weedy-check. The experiment was repeated twice. Visual weed cover and control ratings were collected 4 days after treatment. The experiment had very high weed densities with multiple grass and broadleaf weed species. The weedy check average weed cover percentages were 98% total weeds, 53% grass, 44% broadleaf weeds, 52% large crabgrass (Digitaria sanguinalis (L.), 25% carpetweed (Mollugo verticillata L.), and 14% cutleaf evening primrose (Oenothera laciniata Hill). Total weed control ranged from 0% control (no acetic acid) to 74% control (20% acetic acid, 935 L/ha, & canola oil). Acetic acid was more effective in controlling broadleaf weeds than in controlling grasses. Optimum total grass and crabgrass weed control occurred with 20% acetic acid applied at 935 L/ha, resulting in weed control that ranged from 44% to 63%. Broadleaf weed control was 84% or greater for plots receiving either 10% acetic acid applied at 935 L/ha or 20% acetic acid applied at 187 or 935 L/ha. In addition, 5% acetic acid applied at 187 L/ha provided good cutleaf evening primrose control (77% to 90%). When averaged across application volumes (187 and 935 L/ha) and adjuvants (none, orange oil, and canola oil), weed control increased for all species as acetic acid concentrations increased from 5% to 20%. When averaged across acetic acid concentrations and adjuvants, weed control increased as application volumes increased from 187 to 935 L/ha. Individual comparisons among adjuvants within acetic acid concentrations and application volumes showed little or no advantage to adding either orange oil or canola oil to vinegar spray solutions.