Palmer amaranth started emerging last week.  Some of it is ½ to a 1” tall today April 22. Of course this is just the vanguard of the Palmer that will be coming.  Despite this early Palmer flush typically being less numbers per foot than later emergence events, it is the most important emergence event to control.  The reason it is so important to control is that Palmer amaranth emerging before to slightly after the crop is the most competitive. Therefore, it is imperative that as you start planting cotton or soybean over the next couple of weeks that any existing Palmer amaranth be removed.  This removal can be done through tillage or herbicide.  If tillage is chosen make sure the Palmer is completely buried as larger (>6”) palmer that is partially covered in soil will readily reroot.  This half buried Palmer amaranth is then impossible to control with a herbicide.

The most consistent burndown herbicide to control Palmer amaranth regardless of size is paraquat (Gramoxone Inteon).  In our research over the past several years it has performed well in burning down Palmer amaranth as large as 6” tall. Adding a PSII inhibiting herbicide in with the Gramoxone will provide more consistent control of Palmer.  The PSII inhibiting herbicide depends upon the crop to be planted.  Use atrazine in corn or grain sorghum, metribuzin in soybean and diuron, Cotoran or Caparol in cotton. 

Of course there is still a good amount of corn and grain sorghum yet to be planted.  Gramoxone tankmixed with atrazine will do a great job on Palmer amaranth as well as horseweed.