As the combines cut corn they are often leaving behind a very green field of Palmer amaranth (Picture right). It is not uncommon to find that areas of fields where the corn died early from drought stress have 3 to 6’ tall Palmer in them just now rolling into flowering. These pigweed need to be destroyed as soon as possible. Allowing them to stand for as little as 7 days will allow them to mature enough to produce viable seed.
Good options to control this late flush of Palmer include tillage and the burndown herbicide Gramoxone (paraquat). If tillage is the option please note that it will take aggressive tillage to control >3’ tall Palmer. In many cases where residue is needed to be left on the field; tillage followed within a week to 10 days with Gramoxone should provide adequate control.
Some folks last year only sprayed Gramoxone after corn harvest to control existing pigweed and did not add a residual. In most cases that worked well as the dry fall did not allow much new emergence of Palmer. I would not count on that this year as it is only Mid-August, not late September like last year, and the top soil has some moisture in many cases. Residual herbicides to consider are Valor or Sharpen for fields to go to wheat; Dual Magnum, metribuzin, Sharpen and Valor for fields slated to be planted to soybean; Dual Magnum, metribuzin, simazine and Valor for fields to go back to corn; Dual Magnum and Valor for fields to be planted to cotton.