Pelargonic acid is a fatty acid that occurs naturally in many plants and animals, and is present in many foods we consume. Producers and researchers are interested in pelargonic acid as a broad-spectrum post-emergence, or burn-down herbicide. Field research was conducted in southeast Oklahoma (Lane, OK, Atoka County) to determine the effect of pelargonic acid (nonanoic acid) concentration on weed control efficacy as a burn-down herbicide. One month prior to spraying the weed control treatments the land was cultivated to kill the existing weeds and provide a uniform seed bed for new weed growth. The factorial weed control treatments included three application concentrations of Scythe (57.0% pelargonic acid) applied at 3, 6.5, and 10% and three adjuvants (none, orange oil, and non-ionic surfactant), and two application dates. All herbicide treatments were applied with an application volume of 100 gpa to seedling weeds. The experiment had a high weed density with multiple species of grass and broadleaf weeds. Weed control across species increased as the herbicide concentrations increased from 0 to 10%. At all concentrations applied, pelargonic acid produced greater weed control for a longer time period for the broadleaf weeds than the grass weeds. Visual damage to the weeds was often apparent within a few hours after application. There was a significant increase in weed control when applied to the younger weeds. In this initial trial, pelargonic acid was effective in controlling both broadleaf and grass weeds as a burn-down herbicide, although crabgrass was tougher to control. Additional research will investigate pelargonic acid application methods and weed control efficacy in relationship to controlling additional weed species, and integrating its use into cropping systems.