| The development and release of herbicide-resistant wheat and canola cultivars has raised a variety of questions regarding their potential role in Pacific Northwest crop rotations. This research addressed control of volunteer herbicide-resistant crops, management of imidazolinone-resistant wheat to protect against the development of imidazolinone-resistant weeds, and the tolerance of imidazolinone-resistant wheat cultivars to the herbicide imazamox. Paraquat + diuron controlled glyphosate-resistant wheat and imidazolinone-resistant wheat ≥90%, and glyphosate controlled imidazolinone-resistant wheat 88 to 96% 14 days after treatment (DAT). By 21 DAT, imidazolinone-resistant wheat control with clethodim and quizalofop-P was ≥93%, but the longer time period required for control to reach an acceptable level could increase disease and insect problems associated with volunteer wheat. Volunteer glyphosate-resistant canola was controlled 92 and 97% 14 DAT, and 76 and 98% 21 DAT with paraquat and paraquat + diuron, respectively. In these studies, paraquat + diuron was the best alternative to glyphosate for controlling volunteer herbicide-resistant wheat and canola. Simulation of continuous annual imidazolinone-resistant winter wheat and imazamox herbicide use resulted in the resistant soil seed banks of downy brome, jointed goatgrass, and wild oat surpassing their susceptible soil seed banks in 5, 7, and 10 yr, respectively. A simulation of two consecutive spring crops reduced the initial downy brome susceptible soil seed bank to 19% of the initial density. Based on model simulations, the best management option for reducing the total jointed goatgrass soil seed bank in low precipitation areas is an imidazolinone-resistant winter wheat-fallow rotation. Rotations that include winter and spring crops and rotations that include non group-2 herbicides are the best choice to minimize herbicide resistance selection pressure and reduce the wild oat soil seed bank. The I50 value (imazamox dose that inhibited ALS activity 50%) of the winter wheat Cultvar 'Above' was 54 to 84% higher than the I50 values of 99--420, 99--433, and CV-9804. It is unclear if market class has an effect on ALS sensitivity to imazamox, however pedigree did not influence the level of ALS inhibition by imazamox. Teal 15A, the two gene imidazolinone-resistant spring wheat cultivar, had an I50 value that was 2.3 to 3.2 times greater than the single gene imidazolinone-resistant spring wheat cultivars/lines. The heterozygous imidazolinone-resistant lines had I50 values that were 69 to 81% less than the homozygous lines. In the whole plant dose response, the R 50 values (imazamox dose that reduced biomass 50%) of the susceptible cultivars, Brundage 96 and Conan, were 14.8 to 16.9 times less than the single gene imidazolinone-resistant spring and winter cultivars/lines, whose R 50 values were 1.6 to 1.7 times less than the R50 value of the two gene imidazolinone-resistant spring wheat line, Teal 15A. The results of the in vivo ALS imazamox assays and the whole plant imazamox dose response assay were similar, indicating that the in vivo assay can be used to accurately and quickly compare resistance between imidazolinone-resistant wheat cultivars/lines. |
