Chris Soltau Agronomist Goodhue

by Chris Soltau

The 2017 growing season posed many challenges for weed control, particularly in soybeans.  We have observed in our trade area waterhemp that is resistant to Roundup and Cobra.  We now know we have giant ragweed that is resistant to Roundup and First Rate.

When I first started working in Goodhue in 1995, we had conventional soybeans only.  We did not have Roundup, except for no till burn down.  Looking back, here were the strategies we used then that we do not use as much anymore.

  1. Drill your beans to get a quicker canopy to reduce weed competition.  We went away from this to reduce white mold risk.
  2. Plant your beans at higher populations to get a quicker canopy to reduce weed competition.  We went away from this to reduce white mold risk and increase yields in our AYS A Zones.
  3. Plant your beans after May 10th to use a later tillage pass to wipe out the first flush of weeds.  We have bigger planting equipment now, so we get to the bean acres sooner.  Also, we know that soybeans planted May 1st with fit soils yield tremendous soybeans.

Now we have waterhemp, which germinates later, and the Roundup doesn’t work on all the weeds.  Where do we go next?  I know that vertical tillage and no till has become more prevalent, and it does not replace a tillage pass.  If one isn’t running a field cultivator across the landscape before soybean planting, it needs a burndown herbicide treatment with residual activity.  If you are doing conventional tillage, then spraying or impregnating the pre emerge chemical is fine.  If the soybeans are up before the pre emerge chemical is applied, there are other options for using an early post emerge application.  ALL soybeans should have a two pass program to combat weeds.

If one chooses either the Xtend program or the Roundup program for soybeans for the post emerge weed application, we still have to keep in mind layering our soybean residual to control the waterhemp that will come later.  My favorite choice is Dual Magnum because it works well, and the cost per acre has been the lowest.  This layering is also necessary because we do not canopy as soon as we used to because of wider rows and less plant population.  This past year made it even more difficult when the weeds were tall and the beans were short.  Soybeans treated with Warden RTA and inoculant are faster emerging and healthier, which will also help with canopy closure.

Xtendimax, Roundup, and Flexstar are herbicides.  All herbicides work on specific weeds and need the correct environment to work on killing the weeds along with actively growing weeds.  One thing we all know is never believe a weatherman, and no one has a crystal ball that works.  Farmers and agronomists make calculated decisions to try and maximize herbicide efficacy.  Sometimes herbicides do not work to their fullest potential.  Look at your field after application to make sure that the herbicide did work.  Unfortunately, it isn’t like when Roundup worked and we knew all the weeds were dead.  If you are questioning the control, please bring it to your agronomist’s attention to have them look at it to see if it needs to be resprayed.