By Dwight Lingenfelter
Palmer amaranth regrowth after crop harvest
Palmer amaranth and waterhemp can still set seed yet this fall even after harvest. Make sure to scout fields and control any escaped plants.
With the onset of harvest (especially corn silage and alfalfa) in certain areas of the state it is still necessary to monitor the status of Palmer amaranth and waterhemp once crops are removed. If plants are not cut low enough new shoots can develop at the nodes and produce viable seed yet this fall. Hopefully, no new Palmer germination flushes or much growth will occur in the coming weeks, but it still could happen if the weather stays mild. Palmer plants do not need to be a few feet tall to develop a seed head; even plants less than a foot tall can still set seeds. Consider applications of 2,4-D, dicamba, or Gramoxone if these weed species continue growing or start to germinate after harvest. Tillage can also be a means of control if it is possible.
On another note, if harvesting fields infested with Palmer or waterhemp, make sure to thoroughly clean combines before moving to the next field or farm. Consider moving to a field that will be planted to corn next season since better herbicide options exist in corn to control these weeds. If possible, it is best to harvest contaminated fields last to allow for time this winter for removing components and comprehensively cleaning machines. Since Palmer amaranth and waterhemp seeds are very small it is extremely difficult to remove them, but this task is necessary to prevent their spread.