On Friday Sept. 26, Ag Professional reported that Palmer amaranth had been found in Buffalo County, South Dakota. Early this spring Dr. Bob Hartzler with Iowa State University confirmed that Palmer had been identified at several locations in Iowa.
While the focus is harvest followed directly by harvest this time of year, put this information in a place where you are reminded to consider it once this season is completed. The movement of Palmer amaranth from the Southwest, where it is native, across the entire south and northward has been diligently tracked because of the control difficulty associated with this weed.
As this weed has moved to our neighboring states it becomes all the more important to use the winter months to strengthen your amaranth (red root; water hemp; and especially Palmer) seedling identification skills as well as establish a management strategy should Palmer amaranth be found in your county or your field.
Herbicide resistance observed in Palmer amaranth goes beyond the scope of a single herbicide or site of action to include five different groups identified in the USB supported Take Action bulletin on this weed (http://bulletin.ipm.illinois.edu/wp-content/uploads/2014/03/PalmerAmaranth-2.pdf). The bulletin also identifies possible management strategies if Palmer amaranth is found in your production system.
Strategies include focused efforts to keep fields Palmer amaranth free using effective burndown herbicides and while it is intensive, I would add walking fields and hand eradicating if necessary. Herbicide programs still work but will require the early identification skills as Palmer is tough to control when it is above 3 inches tall.
Again, put this on a back burner during harvest, but plan to hone your identification skills and develop a management strategy once the pressure of harvest is past.
Vigilance is the best option as this weed continues to show adaptation to survive further north. For now get the crop in the bin and when you have a moment, read as much as you can and strategize.
Dr. Paul Meints, Director of Research for Minnesota Soybean