Pelargonic acid weed control: Concentrations, adjuvants, and application timing

Authors: Webber Iii, Charles; SHREFLER, JAMES - OSU, LANE, OK

Submitted to: Proceedings of Horticultural Industry Show
Publication Type: Proceedings
Publication Acceptance Date: 2/8/2007
Publication Date: 5/1/2007
Citation: Webber III, C.L., Shrefler, J.W. 2007. Pelargonic acid weed control: Concentrations, adjuvants, and application timing. Proceedings of the 26th Oklahoma-Arkansas Horticultural Industry Show, January 5-6, 2007, Ft. Smith, Arkansas. 26:145-148.

Interpretive Summary: Pelargonic acid is a fatty acid naturally occurring in many plants, animals, and foods. Pelargonic acid may have applications as a broad-spectrum post-emergence or burn-down herbicide for organic crop production. Field research was conducted in southeast Oklahoma (Lane, OK, Atoka County) to determine the effect of pelargonic acid (nonanoic acid) concentrations, adjuvants, and application timing on weed control efficacy as a burn-down herbicide. Scythe (57.0% pelargonic acid) is a commercial weed control product containing 4.2 lb of pelargonic acid per gallon. The factorial experiment included three application concentrations of Scythe (3, 6.5, and 10% v/v), three adjuvant treatments (none, orange oil, and non-ionic surfactant), and two application dates (1 week apart). All herbicide treatments were applied with a sprayer volume of 100 gallons per acre (gpa). The experiment also included a weedy-check treatment, which served as an untreated control. Weed cover and weed control ratings were collected 10 days after each application date. The weeds present at spraying included large crabgrass, carpetweed, cutleaf evening primrose, spiny amaranth, eclipta, and yellow nutsedge. Application timing and pelargonic acid concentrations were the most important factors in determining weed control. An early application of pelargonic acid, even at the lowest concentration, provided excellent weed control. Delaying applications by just 1 week resulted in a significant decrease in weed control at the lower concentrations. The results demonstrate the importance of applying pelargonic acid when the target weeds are small enough to achieve adequate weed control. This research also demonstrated the potential of pelargonic acid as an organic herbicide.

Technical Abstract: Pelargonic acid is a fatty acid naturally occurring in many plants, animals, and foods. Pelargonic acid has potential as a broad-spectrum post-emergence or burn-down herbicide for organic crop production. Field research was conducted in southeast Oklahoma (Lane, OK, Atoka County) to determine the effect of pelargonic acid (nonanoic acid) concentrations, adjuvants, and application timing on weed control efficacy as a burn-down herbicide. Scythe (57.0% pelargonic acid) is a commercial weed control product containing 4.2 lb of pelargonic acid per gallon. The factorial experiment included three application concentrations of Scythe (3, 6.5, and 10% v/v), three adjuvant treatments (none, orange oil, and non-ionic surfactant), and two application dates (1 week apart). All herbicide treatments were applied with a sprayer volume of 100 gallons per acre (gpa). The experiment also included a weedy-check treatment, which served as an untreated control. Weed cover and weed control ratings were collected 10 days after each application date. The weeds present at spraying included large crabgrass (Digitaria sanguinalis L.), carpetweed (Mollugo verticillata L.), cutleaf evening primrose (Oenothera laciniata Hill), spiny amaranth (Amaranthus spinosus L.), eclipta (Eclipta prostrata L.), and yellow nutsedge (Cyperus esculentus L.). The first application date provided good to excellent weed control across all weed control treatments for total weed, grass, and broadleaf control. The second application date produced significant differences between weed control treatments and between broadleaf and grass control. The 1 week delay between the applications dates resulted in a significant decrease in weed control across most weed control treatments. Only the highest pelargonic acid application concentration maintained excellent control at the later spray date, but only for the broadleafs. Weed control increased for both application dates for total, grass, and broadleaf weed control as pelargonic concentrations increased. The differences in weed control resulting from increasing pelargonic acid concentrations were greater during the second application date, as weed control decreased at the lower concentrations. This research also demonstrated the potential of pelargonic acid as an organic herbicide.