Response of glufosinate-resistant canola to late applications of glufosinate

Previous research has shown that glyphosate applied to glyphosateresistant canola (Brassica napus L.) at later growthstages can reduce yield, particularly if applications are made beyond the six-leaf stage. We questioned whether similar effects could occur in glufosinateresistant canola and therefore, our objective was to characterize the effects of glufosinate application timing on glufosinate-resistant canola. Plots received either a single glufosinate application at the two-leaf, six-leaf, bolt, or early bloom stages or sequential applications at the two-leaf followed by six-leaf, two-leaf followed by bolting, and two-leaf followed by early bloom stages. Significant differences between application timings were observed when glufosinate applications were made beyond the six-leaf stage. In the affected site-years (site and year combinations), delayed applications resulted in reduced plant height (~8%), increased number of aborted pods (~68%), and decreased yield (19%). Increased seeds per pod (~7%) and thousand-seed weight (~29%) were also observed withapplications beyond the six-leaf stage at these site-years. Yield reductions and the increase in aborted pods at applications made beyond the six-leaf stage may be caused by glufosinate contact to reproductive organs, causing herbicide damage consistent witha contact herbicide. Results from this experiment demonstrate that despite engineered glufosinate resistance in glufosinate-resistant canola, late glufosinate applications made beyond the six-leaf stage have the potential to cause marked declines in seed yield and yield components. Although the current label allows for the application of glufosinate at the bolting stage, our results show that glufosinate should not be applied beyond the six-leaf stage in glufosinateresistant canola.