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Title: Scythe (pelargonic acid) weed control in squash

Author
item Webber Iii, Charles
item SHREFLER, JAMES - Oklahoma Agriculture Experiment Station
item BRANDENBERGER, LYNN - Oklahoma State University

Submitted to: Annual Weed Control Research Reports
Publication Type: Experiment Station
Publication Acceptance Date: 3/1/2011
Publication Date: 4/21/2011
Citation: Webber III, C.L., Shrefler, J.W., Brandenberger, L.P. 2011. Scythe (pelargonic acid) weed control in squash. Oklahoma State University, Division of Agricultural Sciences and Natural Resources, Department of Horticulture and Landscape Architecture. Stillwater, Oklahoma. MP-162 p. 20-23.

Interpretive Summary: Organic squash (Cucurbita pepo L.) producers need appropriate herbicides that can effectively provide season- long weed control. Postemergent sequential applications of contact herbicides in organic crops may increase season-long control of weeds in bell peppers to offset the lack of systematic organic herbicides. 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 Scythe (registered trademark) (57% pelargonic acid) applied post-directed at 3, 6, and 9% 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 21, 2010 into raised beds on 36-in centers. The primary weeds included smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.], cutleaf groundcherry (Physalis angulata L.), and spiny amaranth (Amaranthus spinosus L.). Scythe was post-directed applied on July 13 and then reapplied 8 days later (July 21). Grass weed control (78%) and broadleaf weed control (69%) with the 9% Scythe treatment were at their lowest levels at 7 days after the initial spray treatment (DAIT). Smooth crabgrass (98%), cutleaf groundcherry (94%), and spiny amaranth control (94%) control peaked at 9 DAIT (1 day after the sequential treatment) with the 9% application rate. Scythe at 9% also resulted in the greatest crop injury at 9 DAIT (12.5%). The sequential application of Scythe significantly increased grass and broadleaf control at all application rates. The 6 and 9% Scythe treatments produced equivalent squash yields (squash/acre and lb/acre) as the weed-free treatment and greater yields than the weedy check.

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 a potential organic herbicide on weed control efficacy, crop injury, and yields. The experiment included Scythe (registered trademark) (57% pelargonic acid) applied post-directed at 3, 6, and 9% 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 21, 2010 into raised beds on 36-in centers. The primary weeds included smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.], cutleaf groundcherry (Physalis angulata L.), and spiny amaranth (Amaranthus spinosus L.). Scythe was post-directed applied on July 13 and then reapplied 8 days later (July 21). Grass weed control (78%) and broadleaf weed control (69%) with the 9% Scythe treatment were at their lowest levels at 7 days after the initial spray treatment (DAIT). Smooth crabgrass (98%), cutleaf groundcherry (94%), and spiny amaranth control (94%) control peaked at 9 DAIT (1 day after the sequential treatment) with the 9% application rate. Scythe at 9% also resulted in the greatest crop injury at 9 DAIT (12.5%). The sequential application of Scythe significantly increased grass and broadleaf control at all application rates. The 6 and 9% Scythe treatments produced equivalent squash yields (squash/acre and lb/acre) as the weed-free treatment and greater yields than the weedy check.