Wheat cultivars resistant to imazamox will facilitate selective chemical control of many winter annual grass weeds, including jointed goatgrass, downy brome, and feral rye. These three weed species respond differently to imazamox postemergence treatments with feral rye, demonstrating more tolerance than jointed goatgrass or downy brome; therefore, growth chamber studies were conducted to evaluate imazamox absorption in all three weed species and translocation and metabolism in jointed goatgrass and feral rye. Adding nonionic surfactant (NIS) or methylated seed oil increased absorption in jointed goatgrass and feral rye but not in downy brome, compared to imazamox applied alone. Imazamox applied with NIS and urea ammonium nitrate resulted in the highest absorption in each species: 97, 91, and 92% of applied 14C for jointed goatgrass, downy brome, and feral rye, respectively, 48 h after treatment (HAT). Imazamox translocation from the treated leaf was similar for jointed goatgrass and feral rye across seven harvest intervals between 0 and 96 HAT. Shoot tissues of jointed goatgrass and feral rye accumulated 17 and 14% of applied 14C, respectively, by 96 HAT. Differential translocation of imazamox into root tissue was observed within 12 HAT; by 96 HAT, 20% of applied 14C translocated to jointed goatgrass roots compared to 27% for feral rye. Imazamox was readily metabolized in both weed species. At 96 HAT, 73 and 98% of the applied 14C was metabolized in the treated leaves of jointed goatgrass and feral rye, respectively. Metabolism was consistently higher in feral rye than in jointed goatgrass in all plant parts 96 HAT. On a whole-plant basis, metabolism was 25% greater in feral rye than in jointed goatgrass. The differential response of jointed goatgrass and feral rye to foliar applications of imazamox appears to be related to differences in translocation and metabolism but not in absorption.
Nomenclature: Imazamox; downy brome, Bromus tectorum L. BROTE; feral rye, Secale cereale L. SECCE; jointed goatgrass, Aegilops cylindrica L. AEGCY; wheat, Triticum aestivum L.