Protoporphyrinogen oxidase inhibitor mixtures

A method of increasing the activity of a protoporphyrinogen oxidase inhibitor compound of formula (I),

• wherein R is selected from a group consisting of a hydroxyl, a methoxy and an ethoxy, X is selected from the group consisting of CH and nitrogen, and Z is selected from the group consisting of fluorine, chlorine and bromine, or a salt thereof, by applying to an area in need of weed control a protoporphyrinogen oxidase inhibitor compound of formula (I) and a C16 to C18 fatty acid methyl ester adjuvant system, wherein the C16 to C18 fatty acid methyl ester adjuvant system comprises from about 60 to about 99% w/w of C16 to C18 fatty acid methyl ester mixture, from about 0.1 to about 5% w/w of a dodecylbenzene sulfonate salt, from about 0.5 to about 4% w/w of a dodecylbenzene sulfonate salt solvent, from about 0.1 to about 10% w/w of at least one polyoxyethylene plant oil, and from about 0.1 to about 10% w/w of at least one polyoxyethylene sorbitan ester.