Vinegar as a broadcast herbicide for spring-transplanted onions

Authors: Webber Iii, Charles; SHREFLER, JAMES - OSU, LANE, OK

Submitted to: Extension Publications
Publication Type: Experiment Station
Publication Acceptance Date: 9/17/2008
Publication Date: 9/20/2008
Citation: Webber III, C.L., Shrefler, J.W. 2008. Vinegar as a broadcast herbicide for spring-transplanted onions. In: Brandenberger, L. and Wells, L. editors. 2007 Vegetable Weed Control Studies. Oklahoma State University, Division of Agricultural Sciences and Natural Resources, Department of Horticulture & Landscape Architecture. Stillwater, OK. MP-162. p. 20-24.

Interpretive Summary: Organic onion producers need additional organic herbicides that can effectively control weeds that emerge after the crop is transplanted. Field research was conducted in southeast Oklahoma (Lane, Atoka County, OK) to determine the effect of application volume and broadcast applications of vinegar on weed control and onion crop injury. Intermediate day, sweet onion cvs., 'Candy' and 'Cimarron,' were transplanted in mid-March into 2 rows on 6 ft-wide raised beds. The experiment included 6 weed control treatments (2 application volumes, 2 hand-weeding levels, an untreated weedy-check and an untreated weed-free) with 4 replications. Vinegar (20% acetic acid) was applied as an over-the-top broadcast application 39 days after transplanting. The 50 and 100 gpa sprayer application volumes were achieved by adjusting the travel speed while holding all other variables (nozzle size, pressure, and mixture volumes) constant. Within each application treatment (50 and 100 gpa), the weeds were either left in place (weedy-check) or removed by hand-weeding (weed-free check). There were very high weed densities with multiple broadleaf species. In all cases, the application of vinegar increased onion yields compared to the weedy-check for each onion variety. 'Cimarron' produced greater onion yields than 'Candy' in the two 50 gpa vinegar weed control treatments and in the weed-free check that did not received vinegar applications. Broadcast applications of 50 and 100 gpa of 20% acetic acid vinegar can provide good (>80%) to excellent (>95%) broadleaf weed control for up to 5 weeks after application. Although onion plant populations were not reduced, over-the-top broadcast application of vinegar caused severe crop injury within the first few days after treatment.

Technical Abstract: The weed control challenges for onion production are formidable; however, these challenges are even greater for those considering organic crop production. Organic onion producers need additional organic herbicides that can effectively provide post-emergent weed control. Field research was conducted in southeast Oklahoma (Lane, Atoka County, OK) to determine effects of application volume and broadcast applications of acetic acid on weed control efficacy and onion crop injury. Intermediate day, sweet onion cvs. 'Candy' and 'Cimarron' were transplanted in mid-March into 2 rows on 6 ft-wide raised beds. The experiment included 6 weed control treatments (2 application volumes, 2 hand-weeding levels, an untreated weedy-check and an untreated weed-free check) with 4 replications. Vinegar (20% acetic acid) was applied as an over-the-top broadcast application 39 days after transplanting. The 50 and 100 gpa sprayer application volumes were achieved by adjusting travel speed while holding all other variables (nozzle size, pressure, and mixture volumes) constant. Within each application treatment (50 and 100 gpa), the weeds were either left in place (weedy-check) or removed by hand-weeding (weed-free check). There were very high weed densities with multiple broadleaf species. In all cases, application of vinegar increased onion yields compared to the weedy-check for each variety. 'Cimarron' produced greater yields than 'Candy' in the 50 gpa vinegar weed control treatments, and in the weed-free check that did not received vinegar applications. Broadcast applications of 50 and 100 gpa of 20% acetic acid vinegar can provide good (>80%) to excellent (>95%) broadleaf weed control for up to 5 weeks after application. Although onion plant populations were not reduced, over-the-top broadcast application of vinegar caused severe crop injury within the first few days after treatment.