First off, Nipplewort is not an overly common weed species. Finding fields with uniform and relatively dense stands of this weed has proven challenging, and therefore difficult to do replicated herbicide trials. For the farmers that have it though, it does negatively affect crop production, especially in winter cereals where it typically germinates in the fall and becomes quite large by the time postemergence herbicides are applied in the spring. Secondly, nipplewort is tolerant to a lot of herbicides. Therefore, you need to screen a lot of herbicides and tank-mixes in order to find promising treatments that you would want to test under field conditions.
Dr. François Tardif, Peter Smith (University of Guelph) and I started this process in 2002 and we certainly were able to identify herbicides that didn’t work, but thankfully we found a handful of products that gave us reason for optimism, we just needed to tweak some treatments and look at them under more field sites. Finally during the 2020 field season, we have more confidence that one tank-mix in particular, Lontrel XC + Refine SG + non-ionic surfactant, gives us the best opportunity to control nipplewort. We also discovered that some of the newer herbicides that weren’t available back in 2002, aren’t particularly effective.
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