In this study, we tested whether the addition of fatty acid methyl esters (FAME) of edible oils would influence the herbicidal effect of the essential oils (EO) of fiber hemp and peppermint (Mentha × piperita L.) against common lambsquarters, barnyardgrass, and corn. The herbicidal properties of a 2.5% concentration of each EO in water mixtures with FAME were evaluated as sprays in a pot experiment. The oil-FAME mixtures showed phytotoxic effects against common lambsquarters and barnyardgrass expressed by a reduction in plant length and aboveground and root biomass, as measured three weeks after foliar spraying. Corn was the most tolerant species to the tested mixtures. Sunflower FAME alone was safe on corn but reduced the growth of weeds. Peppermint EO alone was the most phytotoxic on all tested species. In conclusion, the mixture of peppermint EO with oilseed rape FAME was the best treatment; however, improvement on Ch. album would be desirable for commercial-level control.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; common lambsquarters, Chenopodium album L. CHEAL; common sunflower, Helianthus annuus L.; corn, Zea mays L.; hemp, Cannabis sativa L.; peppermint, Mentha × piperita L. Huds. var. officinalis Sole, f. rubescens Camus; rape, Brassica napus L.; soybean, Glycine max (L.) Merr.