ARS | Publication request: Interaction of Glyphosate and Pelargonic acid in Ready-To-Use Weed Control Products

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2008
Publication Date: October 1, 2009
Repository URL: http://hdl.handle.net/10113/39428
Citation: Wehtje, G., Altland, J.E., Gilliam, C. 2009. Interaction of Glyphosate and Pelargonic acid in Ready-To-Use Weed Control Products. Weed Technology. 23:544-549.

Interpretive Summary: Pelargonic acid is often added to glyphosate products to improve weed control. Glyphosate generally provides excellent weed control over a broad spectrum of species, however, control can take up to two weeks to manifest. Addition of pelargonic acid causes more rapid burn-down of weeds, and presumably improves customer satisfaction that the herbicide is effective. The objective of our research was to determine the short and long-term weed control effects of adding pelargonic to glyphosate. Our results demonstrated that adding pelargonic acid improved control in only two species, and that control was only manifested early in the evaluation period. Conversely, addition of pelargonic acid had either no effect or a detrimental effect on long-term weed control across four weed species. We conclude that the addition of pelargonic acid to glyphosate is not warranted or justified.

Technical Abstract: Glyphosate-based, ready-to-use weed control products often contain pelargonic acid (PA) in addition to glyphosate. However it remains unclear what benefit (if any) this combination provides. Greenhouse experiments using longstalked phyllanthus, large crabgrass, prostrate spurge and yellow nutsedge were conducted to determine whether the addition of PA improved efficacy compared to glyphosate alone. Glyphosate was applied at a series of rates, ranging from 0.11 to 1.12 kg ae/ha, either alone or with an equal rate of PA. The addition of PA to glyphosate was synergistic only in two of the four species, and this synergism was manifested only in the degree of early visual injury. Conversely, longer-term control and control of regrowth, depending upon the species, was either not affected or reduced by the addition of PA. We conclude that the addition of PA to glyphosate in ready-to-use weed control products is not warranted nor justified.