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United States Department of Agriculture

Agricultural Research Service

Title: Scythe (57% pelargonic acid) broadcast application for broadleaf weed control in spring-transplanted onions

Authors
item Webber, Charles
item Shrefler, James - OSU, LANE, OK

Submitted to: Extension Publications
Publication Type: Experiment Station
Publication Acceptance Date: January 15, 2009
Publication Date: February 7, 2009
Citation: Webber III, C.L., Shrefler, J.W. 2009. Scythe (57% pelargonic acid) broadcast application for broadleaf weed control in spring-transplanted onions. In: Brandenberger, L., Wells, L., editors. 2008 Vegetable Trials Report, Oklahoma State University, Division of Agricultural Sciences and Natural Resources, Department of Horticulture & Landscape Architecture. Stillwater, OK. MP-164, p. 59-61.

Interpretive Summary: Producers using organic methods for onion production need organic herbicides that will effectively provide post-emergent weed control. Field research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the effect of broadcast over-the-top application of Scythe (57% pelargonic acid) on weed control efficacy, crop injury and yields. Intermediate day, sweet onion cvs. 'Candy' and 'Cimarron' were transplanted on March 20, 2008 into 2 rows per 6 ft-wide by 10 ft-long raised beds. The experiment included 8 weed control treatments (3 application rates at 2 hand-weeding levels, plus an untreated weedy-check and an untreated weed-free) with 4 replications. Nutsedge (Cyperus esculentus L.) and grass weeds were removed from all plots, including the weedy-check, to investigate the impact of pelargonic acid on the broadleaf weeds. Scythe at three rates, 3, 5, and 7% v/v, over-the-top was broadcast applied 44 days after transplanting using a tractor mounted CO**2 sprayer equipped with four extended range, stainless steel, 0.20 gallons/min nozzles on 20-inch spacings at a spraying height of 19 inches at 100 gpa. The two weed control treatments within each application rate (7.5, 10% and 15% v/v) involved no hand-weeding, where the uncontrolled weeds were allowed to grow, or a season-long hand-weeding, where all weeds were removed. Broadleaf weed control for the all application rates were acceptable (equal to or greater than 80%) until 18 days after treatment (DAT). Scythe applied at 5 and 7% was 89% or greater weed control until harvest. Weed control with 3% Scythe was less than 5 and 7% Scythe at 10, 18, and 33 DAT. The greatest onion injury was recorded 2 DAT for 5 and 7% Scythe, and at 10 DAT for 3% Scythe. Scythe crop injury increased as application rate increased and decreased to 0% injury at 18 DAT. Application of Scythe decreased onion yields compared to the untreated weed-free control. 'Cimarron' and 'Candy' yields were greater than the untreated weedy-check when Scythe was applied at 3 and 5%. Scythe applied at 7% reduced yields were equal to or less than the untreated weedy-check. When examining broadleaf weed control, crop injury, and yields the 5% Scythe application has the best potential for use in spring-transplanted onions.

Technical Abstract: Although previous studies yielded important information concerning use of pelargonic acid as a potential organic herbicide, further research is indicated to increase the understanding of the relationship among application volumes, weed species, and weed maturity on herbicidal efficacy and crop injury. Field research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the effect of application volume and broadcast application of pelargonic acid on weed control efficacy, crop injury and yields. Intermediate day, sweet onion cvs. ‘Candy’ and ‘Cimarron’ were transplanted on March 20, 2008 into 2 rows per 6 ft-wide by 10 ft-long raised beds. The experiment included 8 weed control treatments (3 application rates at 2 hand-weeding levels, plus an untreated weedy-check and an untreated weed-free) with 4 replications. Nutsedge (Cyperus esculentus L.) and grass weeds were removed from all plots, including the weedy-check, to investigate the impact of pelargonic acid on the broadleaf weeds. Scythe (57% pelargonic acid) at three rates, 3, 5, and 7% v/v, over-the-top was broadcast applied 44 days after transplanting using a tractor mounted CO**2 sprayer equipped with four extended range, stainless steel, 0.20 gallons/min nozzles on 20-inch spacings at a spraying height of 19 inches at 100 gpa. The two weed control treatments within each application rate (7.5, 10% and 15% v/v) involved no hand-weeding, where the uncontrolled weeds were allowed to grow, or a season-long hand-weeding, where all weeds were removed. Broadleaf weed control for the all application rates were acceptable (equal to or greater than 80%) until 18 days after treatment (DAT). Scythe applied at 5 and 7% was 89% or greater weed control until harvest. Weed control with 3% Scythe was less than 5 and 7% Scythe at 10, 18, and 33 DAT. The greatest onion injury was recorded 2 DAT for 5 and 7% Scythe, and at 10 DAT for 3% Scythe. Scythe crop injury increased as application rate increased and decreased to 0% injury at 18 DAT. Application of Scythe decreased onion yields compared to the untreated weed-free control. ‘Cimarron’ and ‘Candy’ yields were greater than the untreated weedy-check when Scythe was applied at 3 and 5%. Scythe applied at 7% reduced yields were equal to or less than the untreated weedy-check. When examining broadleaf weed control, crop injury, and yields the 5% Scythe application has the best potential for use in spring-transplanted onions.

Last Modified: 10/22/2014
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