October 16, 2018

DICAMBA FOR WEED CONTROL IN SOYBEANS: IT’S ONLY A BIT

by Matt Thoreson  MattT@agpartners.net

Cordless drills and drivers have become so popular, nearly every shop has at least one.  But they aren’t much good without the correct bit to get the fastener secured or loosened.  There are a bunch of sizes and types of bits; philips, flat, torx, and sockets to name a few.  Each one has its own appropriate use.  Together, the bit and driver combination work great.  But for most tasks using only one individually leads to struggles.  Using the wrong combination can end in failure.  Using the right combination incorrectly can have far worse consequences.

The same thing is true when it comes to weed control options for soybeans.  Weed control in soybeans has become very complex.  Weed species and emergence timing, herbicide resistance and crop stage at application (the fastener) are all things that need to be considered when choosing a herbicide program.  We need a program (the driver) with the right products and application timing (the bit).  Soil residual herbicides like Sonic and Dual, and PPO herbicides like Flexstar are products, or “bits”, that are appropriate and necessary for specific weeds.  But for many soybean acres that may not be enough.

Now, an emerging technology is an option for weed control in soybeans.   Xtendimax, Engenia, and FeXapan are formulations of the broadleaf herbicide Dicamba (successfully used for many years in grass crops) and available to use on Dicamba-tolerant soybeans.  A new “bit” so to speak.  It’s shiny and new, and at first glance may look like it would replace some of the older, more worn “bits” in the toolbox.  These products do kill broadleaf weeds, and are very safe on appropriate varieties.  But this “bit” has use directions that are unique from the other “bits” we have been using.  Among those are directions to prevent off-target movement:

  • These products may only be applied using approved nozzles, applied when wind is between 3 and 10 mph, applied only between sunrise and sunset, and 24 hours before rainfall;
  • These products must NOT be applied when wind is blowing toward a neighboring sensitive crop, NOT applied during a field-level temperature inversion, NOT applied after June 20th, and NOT applied when air temperature is, over or is forecasted to be, over 85 degrees.

Dicamba is not a bad product choice for use in Dicamba-tolerant soybeans.  The largest problem that exists is that due to use restrictions, its application opportunities are limited and may not be available as an option at all for your operation’s needs.   We need to keep using our existing tools, our familiar chemistries, and perhaps use Dicamba as a supplemental part of the whole strategy. A successful broadleaf weed control program in soybeans is so complex that no one tool will provide satisfactory results, no matter which tool is used.

If growers want to keep Dicamba as an option for broadleaf weed control in soybeans, it has to be used correctly so that it remains effective and does not become a problem by moving off-target and injuring susceptible plants.  These products and this technology will be closely watched and heavily scrutinized locally, regionally and nationally.  The only way for this technology to be available beyond 2018 is to use it correctly and responsibly.  If it’s not, it may end up as nothing more than a useless bit.