Fate of acifluorfen and lactofen in common waterhemp (Amaranthus rudis) resistant to protoporphyrinogen oxidase–inhibiting herbicides

Studies were conducted to determine acifluorfen and lactofen absorption, translocation, and metabolism in protox-inhibiting herbicide-susceptible and -resistant common waterhemp. Acifluorfen and lactofen absorption was similar in both biotypes. Herbicide absorption was 12% in both susceptible and resistant common waterhemp 6 h after treatment (HAT). Absorption increased to 32 and 42% in susceptible and resistant plants, respectively, at 72 HAT. Translocation was similar in both biotypes for both herbicides. Herbicide translocation out of the treated leaf ranged between 5 and 15%. In a separate study, resistant common waterhemp plants were treated with acifluorfen or lactofen, alone or with tridiphane. Acifluorfen or lactofen injury to resistant common waterhemp was not altered with the addition of tridiphane. Treatments of 14C-acifluorfen or lactofen on susceptible and resistant common waterhemp resulted in similar lactofen metabolism in both biotypes, but acifluorfen was not metabolized in either biotype within 24 HAT. This data indicate that differences in herbicide absorption, translocation, or metabolism are not the mechanism of common waterhemp resistance to protox-inhibiting herbicides.