Managing Palmer Amaranth and Grass Burndown Escapes

Picture 1. Grass and Palmer amaranth escaping paraquat burndown in emerged cotton

There have been numerous fields where goosegrass, junglerice and Palmer amaranth were not controlled at burndown and the crop has emerged. In some cases, the wet weather delayed burndown to where Palmer amaranth and those grasses were too large to be effectively controlled with one pass of Gramoxone (Picture 1). In other cases, tillage used to help speed up field drying or to build beds partially buried pigweed and grasses which make effective burndown from Gramoxone very problematic (Picture 2). In a few cases, dicamba and glyphosate were used for burndown and they did not control those weeds due to resistance (Picture 3).

Picture 2. Goosegrass and Palmer amaranth that was partially buried during burndown escaping paraquat

The best way to go about trying to control those weeds is to assess what is the biggest problem in the field and target that or those weeds first. If it is goosegrass and junglerice then go with a robust rate of clethodim.

In fields where some Palmer amaranth is in the mix then Liberty can be tankmixed in with clethodim to help on Palmer amaranth without negatively impacting the grass control. Liberty will control smaller Palmer amaranth and set back larger Palmer amaranth. Then a follow-up application of either Liberty or dicamba within 10 days of that application should control at least some of that population. Later in cotton, a hooded application of Gramoxone may be needed to get complete control for at least those pigweeds in the row middles.

Picture 3. Palmer amaranth recovering after a burndown with dicamba and glyphosate

Another option some will use is XtendiMax or Engenia mixed with clethodim. Those dicamba products will wrap up but not control those big pigweeds or even small pigweeds where resistance is present. However, a Liberty application shortly after that dicamba application should provide fair control of escapes.

Though clethodim is a better choice than glyphosate, clethodim will not be as effective controlling grass when tankmixed with dicamba. In our research, that tankmix reduced junglerice control 11% compared to an application of clethodim alone. Additionally in the same study, adding glyphosate to dicamba reduced junglerice control 27% compared to glyphosate applied alone.