Repeated application of acetyl-coA carboxylase–inhibiting herbicides, such as sethoxydim, may select for resistant (R) weed populations, making a rapid and reliable seedling bioassay a useful tool. Such a bioassay was developed to determine shoot and root responses of giant foxtail seedlings to sethoxydim. Root and shoot elongation of susceptible (S) and R giant foxtail seedlings was measured at 3 and 6 d after exposure to 0.1 to 100 mg/L sethoxydim. A bioassay concentration of 10 mg/L sethoxydim easily discriminated between S and R biotypes of giant foxtail at 6 d after exposure, with R:S shoot and root growth ratios of 3 and 10, respectively.
Nomenclature: Sethoxydim; giant foxtail, Seteria faberi Herrm. #3 SETFA.
Additional index words: ACCase inhibitor, bioassay.
Abbreviations:ACCase, acetyl-coA carboxylase; DAT, days after treatment; R, resistant; S, susceptible.
