Control of common sowthistle ( <i>Sonchus oleraceus</i> ) and prickly lettuce ( <i>Lactuca serriola</i> ) with PSII-inhibiting herbicides in a novel breeding line of metribuzin-tolerant lentil ( <i>Lens culinaris</i> )

Abstract In southern Australia, sowthistle and prickly lettuce are difficult to control when they grow among pulse crops because few postemergence herbicide options exist to control them and resistance to herbicides that inhibit acetolactate synthase (ALS) has become widespread. The introduction of new herbicide-tolerance traits to these crops is one possible avenue for improving control options. This study evaluated ways to control ALS inhibitor–resistant common sowthistle and prickly lettuce in a novel breeding line of metribuzin-tolerant lentil being developed in Australia. Field experiments conducted over 3 site-years in South Australia aimed to evaluate various rates and application timings of metribuzin, with and without the postemergence addition of diflufenican, compared to preemergence terbuthylazine applications. Herbicide treatments achieved significant levels of control of both common sowthistle and prickly lettuce compared to untreated control plots, and there was no negative effect of these treatments on lentil establishment or yield, despite two sites experiencing environmental conditions that were conducive to crop damage by the herbicides. Greater control was obtained when higher rates of metribuzin were applied post-sowing preemergence and after the postemergence application of diflufenican. Terbuthylazine treatments also performed well compared to the untreated control; however, terbuthylazine was not as effective as the higher rates of metribuzin. These results indicate that the introduction of a metribuzin-tolerant lentil cultivar will provide an effective in-crop broadleaf weed control option while also avoiding some of the damage associated with currently available herbicides.