There is no doubt that Roundup resistance weeds have become an issue for some of Rowan County farmers.  If not an issue now, it will be soon enough. Many farmers that I have met in the past months have asked me one question.  “How can I kill it?”  First, do not be afraid to walk out in the field and spend a few hours pulling the plant up by hand.  Though time consuming and labor intensive, it is a sure way to free your fields of the weed and thus reducing the amount of plants that may return next year.  If a small amount of resistant weeds have been spotted, hand pulling the weed is your best option.
 
However, I understand that this is not the answer farmers want to hear.  Therefore, my second answer is to use a chemical with a different mode of action (MOA).  What is a MOA?  MOA describes the direction or path by which the chemical will attack the plant at the cellular level.  Glyphosate (a glycine herbicide) when applied inhibits the plants ability to form chemical compounds derived of amino acids which are crucial to a plants growing ability.  Plants in North Carolina such as horseweed or Palmer amaranth have naturally evolved to resist the affect of glyphosate.  It is recommended that farmers who are faced with resistant weeds use a tank mix.  It is crucial to use two different chemicals with two different MOAs, wherefore the plants naturally growing process can be disrupted at different cellular processes.  Consider the MOA of each herbicide used when mixing your tank and always follow label recommendations.  Furthermore, take into account that pre-plant and pre-emergent herbicides are the most effective herbicides against resistance weeds.  If a weed is allowed to grow 6 inches or taller, the effectiveness of the herbicides used will decrease dramatically.  Applying pre-plant and pre-emergent herbicides 
 
Overall, it is our ultimate goal to not have such resilient weeds in our fields.  Over the past few years, researchers have developed the PAMS approach to dealing with not only resistant weeds but for any pest in general.  PAMS stands for Prevention, Avoidance, Monitoring, and Suppression.  Prevention tells us to take steps such as cleaning farm equipment when traveling from field to field.  Avoidance can be practiced when the pest is present but the impact is low.  Avoidance is crop rotation, choosing cultivars with genetic resistances, using trap crops or pheromone traps.  Monitoring is one of the most important steps to follow.  It is vital to know what pest you are dealing with.  Take the time to walk troubled fields or areas where you know pest can occur.  Keep records or create pest maps.  This will help in producing a plan of action or crop selection for the future.
 
Finally, if the previous steps are not successful, cultural practices should be used such as no-till, stripe till, or the use of narrow or wide rows.  Chemical controls are important in this stage as well.  Identify the correct pest and always follow application instructions located on the label before apply a chemical suppression.
 
For more information on herbicide resistance or for herbicide formulations, please call Scott Tilley at 704-216-8970 or email at scott_tilley@ncsu.edu.