The most prevalent weeds in Wisconsin in 2019 were waterhemp and giant ragweed, says Tryston Beyrer, WinField United agronomist, adding that no-till farmers may have also had marestail and other winter annual weeds to contend with.
Weather conditions made it difficult for farmers to get preemergence herbicides applied in a timely manner, although many times early postemergence applications or residual applications worked well. Timely scouting and managing of weeds when they were small was key.
Hopefully, no-till farmers were able to take care of marestail with a fall burndown; if not, they’ll need to do an early spring burndown, says Beyrer. The good thing about a spring burndown is that it comes with some residual chemistries, so to a degree farmers can lessen the pressure of applying a herbicide right at planting. Instead, they can apply an early postemergence herbicide to spread out some of their risk and workload.
For management of both waterhemp and giant ragweed in 2020, Beyrer recommends starting with a preemergence herbicide plan. There are three main reasons to apply a preemergence herbicide. One is to buy some time if farmers can’t get back into the field promptly. Two, as weeds emerge, they compete with the crop for sunlight and nutrients. Three, though many preemergence herbicide programs aren’t perfect, they can help reduce weed pressure prior to a postemergence application, says Beyrer.
When selecting preemergence and postemergence herbicides, Beyrer encourages farmers to consider using multiple effective modes of action. Waterhemp specifically has known resistance to at least six different herbicides including glyphosate, ALS, PS II and PPO chemistries, so farmers should incorporate other chemistries to manage it. If farmers do have some of those troublesome weeds, Beyrer recommends selecting a trait platform that helps adequately manage them.