Pelargonic acid as a post-directed herbicide for onions

Authors: Webber Iii, Charles; SHREFLER, JAMES - Oklahoma Agriculture Experiment Station; BRANDENBERGER, LYNN - Oklahoma State University; Davis, Angela

Submitted to: Proceedings of Horticultural Industry Show
Publication Type: Proceedings
Publication Acceptance Date: 12/15/2011
Publication Date: 5/6/2012
Citation: Webber III, C.L., Shrefler, J.W., Brandenberger, L.P., Davis, A.R. 2012. Pelargonic acid as a post-directed herbicide for onions. Proceedings of Horticultural Industry Show, January 5-6, 2012, Tulsa, Oklahoma. p. 148-151.

Interpretive Summary: Oklahoma producers are interested in sweet onion (Allium cepa L.) as an alternative crop to diversify production. Onions do not compete well with weeds due to their slow growth rate, short height, non-branching plant structure, low leaf area, and shallow root system. Weed control challenges for onion production are even greater for those considering organic crop production. Research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the impact of a potential organic herbicide on weed control efficacy, crop injury, and yields. The experiment included 5 weed control treatments (1 herbicide applied at 3 rates) with sequential applications separated by 8 days, plus an untreated weedy-check and an untreated weed-free check) with 6 replications. The herbicide, Scythe (registered trademark) (57% pelargonic acid), was applied at 3, 6, and 9% v/v at 40 gpa with a post-directed application. An intermediate day, sweet onion, cv. 'Candy,' was transplanted on April 5, 2010 into 2 rows per 6 ft-wide raised beds. Each plot consisted of two onion rows per 10 ft length of bed. Weed control (total, evening primrose, smooth crabgrass, and yellow nutsedge) increased as Scythe rate increased from 3 to 9% v/v. Initial, 1 day after initial treatment (DAIT), control for the total, evening primrose, and smooth crabgrass ratings were similar, but the smooth crabgrass control quickly declined after 1 DAIT. Injury increased as Scythe rate increased with a spike in injury following sequential application at 8 DAIT. All Scythe treatments produced significantly less marketable onions and weight/acre. Although onion injury was reduced compared to previous research using the over-the-top broadcast applications of potential organic herbicides, onion yields in this study were unacceptable due to the lack of weed control and crop injury. This research benefits the organic onion industry by demonstrating the need for additional weed control methods to enhance weed control, while reducing crop injury. Further research should combine use of corn gluten meal or mustard meal as preemergence herbicides combined with between row applications of post-emergence organic herbicides.

Technical Abstract: Organic onion producers need appropriate herbicides that can effectively provide post-emergent weed control. Research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the impact of a potential organic herbicide on weed control efficacy, crop injury, and yields. The experiment included 5 weed control treatments (1 herbicide applied at 3 rates) with sequential applications separated by 8 days, plus an untreated weedy-check and an untreated weed-free check) with 6 replications. The herbicide, Scythe (registered trademark) (57% pelargonic acid), was applied at 3, 6, and 9% v/v at 40 gpa with a post-directed application. An intermediate day, sweet onion, cv. 'Candy,' was transplanted on April 5, 2010 into 2 rows per 6 ft-wide raised beds. Each plot consisted of two onion rows per 10 ft length of bed. Weed control (total, evening primrose, smooth crabgrass, and yellow nutsedge) increased as Scythe rate increased from 3 to 9% v/v. Initial, 1 day after initial treatment (DAIT), control for the total, evening primrose, and smooth crabgrass ratings were similar, but the smooth crabgrass control quickly declined after 1 DAIT. Injury increased as Scythe rate increased with a spike in injury following sequential application at 8 DAIT. All Scythe treatments produced significantly less marketable onions and weight/acre. Although onion injury was reduced compared to previous research using over-the-top broadcast applications of potential organic herbicides, onion yields in this study were unacceptable due to the lack of weed control and crop injury. Further research should combine the use of corn gluten meal or mustard meal as preemergence herbicides combined with between row applications of post-emergence organic herbicides.