Weed control in yellow squash using sequential postdirected applications of pelargonic acid

Authors: Webber Iii, Charles; TAYLOR, MERRITT - Oklahoma State University; SHREFLER, JAMES - Oklahoma State University

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2013
Publication Date: 2/1/2014
Publication URL: https://handle.nal.usda.gov/10113/59439
Citation: Webber III, C.L., Taylor, M.J., Shrefler, J.W. 2014. Weed control in yellow squash using sequential postdirected applications of pelargonic acid. HortTechnology. 24(1):25-29.

Interpretive Summary: Pelargonic acid is a fatty acid naturally occurring in many plants and animals and present in many foods. Pelargonic acid injures and kills plants by destroying the cell membranes, causing rapid desiccation of plant tissues. Chloroplast bleaching is seen within a short time after application. Research was conducted in southeast Oklahoma (Atoka County, Lane, OK) during 2010 and 2011 to determine the impact of pelargonic acid, a naturally derived herbicide, on weed control efficacy, crop injury, and squash (Cucurbita pepo L.) yields. The experiment included Scythe(R) (57% pelargonic acid) applied at three application rates, plus an untreated weedy-check and an untreated weed-free check with 4 replications, on raised beds of 'Enterprise' yellow squash. Scythe was applied each year in mid-July and then reapplied 8 days later. The greatest control of smooth crabgrass, broadleaf weed, and yellow nutsedge was observed with the 9% Scythe treatment at 9 days after the initial spray treatment. Scythe at 9% provided equal or slightly greater smooth crabgrass and broadleaf (cutleaf groundcherry and spiny amaranth) control compared to the 6% treatment, and consistently greater control than the 3% rate and the weedy check. Yellow nutsedge control with Scythe was less effective than it was with smooth crabgrass and broadleaf weeds. However, increasing the Scythe application rate increased the injury rating to the squash at 1 and 3 days after each application. The 6% Scythe treatment produced the highest squash yields and fruit number compared to either the 3 or 9% Scythe application and equivalent yields and fruit number as the hand-weeded weed-free treatment. The 6% Scythe applied in a timely sequential application has the potential to provide good weed control with minimal crop injury, resulting in yields equivalent to weed-free hand-weeding conditions.

Technical Abstract: Squash (Cucurbita pepo L.) producers would benefit from appropriate herbicides that can effectively provide season-long weed control. Research was conducted in southeast Oklahoma (Atoka County, Lane, OK) during 2010 and 2011 to determine the impact of a naturally derived herbicide on weed control efficacy, crop injury, and squash yields. The experiment included Scythe(R) (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, 'Enterprise', was direct-seeded in single rows 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.). Scythe was post-directed applied each year in mid-July and then reapplied 8 days later. The greatest smooth crabgrass control (98%), broadleaf weed control (94%), and yellow nutsedge (41%) was observed with the 9% Scythe treatment at 9 days after the initial spray treatment (DAIT) [1 day after sequential treatment (1 DAST)]. The Scythe at 9% provided equal or slightly greater smooth crabgrass and broadleaf (cutleaf groundcherry and spiny amaranth) control compared to the 6% treatment, and consistently greater control than the 3% rate and the weedy check. Yellow nutsedge control with Scythe was less effective than it was with smooth crabgrass and broadleaf weeds. Yellow nutsedge control peaked at 9 DAIT (1 DAST) with 9% Scythe (41%). As the rate of Scythe increased from 3 to 9%, the yellow nutsedge control also increased significantly for all observation dates, except for 28 DAIT. Increasing the Scythe application rate increased the injury rating at 1 and 3 days after each application (1 and 3 DAIT, 1 and 3 DAST). The maximum crop injury was observed for each application rate at 9 DAIT (1 DAST) with 4.4, 8.0, and 12.5% injury for Scythe 3, 6, and 9%, respectively. The 6% Scythe treatment produced the highest squash yields (kg/ha) and fruit number (fruit/ha) compared to either the 3 or 9% Scythe application and equivalent yields and fruit number as the hand weeded weed free treatment. The 6% Scythe applied in a timely sequential application has the potential of providing good weed control with minimal crop injury resulting in yields equivalent to weed free hand weeding conditions.