The release of apical dominance by the physical destruction in situ of the apical meristem and associated leaf primordia (decapitation) promoted the growth of tillers in non-herbicide-treated wild oat plants, as indicated by increased tiller lengths and fresh weights. At 96 h after [~4C] herbicide treatment following decapitation, the absorption of [lac]imazamethabenz and total translocation of radioactivity were respectively increased by 28% and 49%. By 96 h after [14C]imazamethabenz application, the radioactivity detected in the roots of decapitated plants was 45% higher than that in the roots of nondecapitated plants while the radioactivity in tillers of decapitated plants was 2.6-fold that in tillers of intact plants. Decapitation together with foliar spraying of imazamethabenz at 200 g hafurther reduced tiller fresh weight, greatly decreased the total tiller number, and thereafter significantly increased overall phytotoxicity by 32% as measured by total shoot fresh weight. The results of this study support the hypothesis that main shoot apical dominance limits translocation of applied imazamethabenz to lateral shoots, rendering tillers less susceptible to growth inhibition by the herbicide.
Wild oat (Avena fatua L.) is one of the most common, persistent agricultural weeds in the prairies of Canada. Imazamethabenz, (-)-2-[4,5-dihydro-4methyl-4-(1-methylethyl)-5-oxo-lH-imidazol-2-yl)-4 (and 5)-methylbenzoic acid (3:2), is a selective postemergent herbicide for control of wild oat and several other weeds in cereal crops (Kneeshaw et al. 1983, Shaner et al. 1982). The recommended * Author for correspondence.