Potential organic herbicides for squash production: Pelargonic acid herbicides AXXE (registered trademark) and Scythe (registered trademark)

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

Submitted to: Extension Publications
Publication Type: Experiment Station
Publication Acceptance Date: 3/15/2012
Publication Date: 4/1/2012
Citation: Webber III, C.L., Shrefler, J.W., Brandenberger, L.P., Davis, A.R. 2012. Potential organic herbicides for squash production: Pelargonic acid herbicides AXXE (registered trademark) and Scythe (registered trademark). 2011 Vegetable Trial Report. Oklahoma State University, Division of Agricultural Sciences and Natural Resources, Department of Horticulture & Landscape Architecture. Stillwater, OK. MP-164. p. 41-43.

Interpretive Summary: Organic squash (Cucurbita pepo L.) producers need appropriate herbicides that can effectively provide season- long weed control. Research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the impact of potential organic herbicides on weed control efficacy, crop injury, and yields. The experiment included AXXE (registered trademark) (65% pelargonic acid) and Scythe (registered trademark) (57% pelargonic acid) applied post-directed at 1.5, 3, 5, and 10% v/v application rates, plus an untreated weedy-check and an untreated weed-free check with 4 replications. Yellow squash, cv. 'Enterprise,' was direct-seeded on June 27, 2011 into raised 91-cm centered beds. The primary weeds included smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.], cutleaf groundcherry (Physalis angulata L.), and spiny amaranth (Amaranthus spinosus L.). Axxe and Scythe were post-directed applied on July 14 and then the 1.5, 3, and 5% v/v treatments were reapplied 11 days later (July 25). Weed control (total, broadleaf, and grass) increased as application rate increased, producing a minimum of 99% control 1 day after initial treatment (DAIT) for the 10% v/v rate for each herbicide. The single application of each herbicide at 10% v/v performed similarly across weed control rates (12 to 41 DAIT) to the sequential application of 5% v/v. Squash injury increased as application rates increased. The 10% v/v application rates produced the most squash injury at 1 DAIT with the 5% v/v producing the greatest injury at 12 DAIT following the sequential application. Squash yields (fruit/acre and t/acre) increased up to the 5% v/v rate and declining with 10% v/v, indicating that the greater initial injury produced season-long yield reductions. All herbicide applications produced as good, or greater, yields than the weedy-check. The 5% v/v sequential applications provide additional flexibility in the timing of the weed control treatments. Organic producers can benefit from the demonstrated effectiveness of post-directed herbicide application for weed control in organic squash production. Additional research should focus on fine-tuning the herbicide application to control specific weeds at various maturity levels and sizes.

Technical Abstract: Organic squash (Cucurbita pepo L.) producers need appropriate herbicides that can effectively provide season- long weed control. Research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the impact of potential organic herbicides on weed control efficacy, crop injury, and yields. The experiment included AXXE (registered trademark) (65% pelargonic acid) and Scythe (registered trademark) (57% pelargonic acid) applied post-directed at 1.5, 3, 5, and 10% v/v application rates, plus an untreated weedy-check and an untreated weed-free check with 4 replications. Yellow squash, cv. 'Enterprise,' was direct-seeded on June 27, 2011 into raised 91-cm centered beds. The primary weeds included smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.], cutleaf groundcherry (Physalis angulata L.), and spiny amaranth (Amaranthus spinosus L.). Axxe and Scythe were post-directed applied on July 14 and then the 1.5, 3, and 5% v/v treatments were reapplied 11 days later (July 25). Weed control (total, broadleaf, and grass) increased as application rate increased, producing a minimum of 99% control 1 day after initial treatment (DAIT) for the 10% v/v rate for each herbicide. The single application of each herbicide at 10% v/v performed similarly across weed control rates (12 to 41 DAIT) to the sequential application of 5% v/v. Squash injury increased as application rates increased. The 10% v/v application rates produced the most squash injury at 1 DAIT with the 5% v/v producing the greatest injury at 12 DAIT following the sequential application. Squash yields (fruit/acre and t/acre) increased up to the 5% v/v rate and declined with 10% v/v, indicating that the greater initial injury produced season-long yield reductions. All herbicide applications produced as good, or greater, yields than the weedy-check. The 5% v/v sequential applications provide additional flexibility in the timing of the weed control treatments. Additional research should focus on fine-tuning the herbicide application to control specific weeds at various maturity levels and sizes.