Management Of Horseweed Escapes Prior To Planting

JACKSON, TENN.
   Horseweed (marestail) still present in fields after dicamba and glyphosate applied 2 to 3 weeks ago has been the most common call of the week. Many want to know if the twisted up horseweed will go ahead and die or if it will recover.
   Some of this can be determined by pulling some individual horseweed plants out of these fields and breaking the stem in half. If the stem is beginning to discolor or hollow out, my experience would be that it will go ahead and die. If that stem remains a bright solid white then it could recover to some extent. Often, but not always, these recovering horseweed are very slow growing and not overly competitive. The question then follows should I apply another burndown application prior to planting my cotton or soybean to remove this surviving horseweed?













   If the field is to be planted to a glufosinate-tolerant cotton then these surviving horseweed can easily be controlled with Liberty early postemergence. The only reason to follow up with, say, a paraquat application is if there is any newly emerged horseweed or Palmer amaranth. If the field is going to non-glufosinate tolerant cotton and there is a considerable population of horseweed that could survive then a follow up application of paraquat or Liberty is a good way to go. On the other hand, if the population of this surviving horseweed is minimal then an application of Envoke or even Staple in season will likely keep them in check.
   Similarly, if the field is going to be planted to Liberty Link soybean the surviving horseweed can be easily controlled with Liberty in crop when the weather is warm. If however, the field is going to be planted to Roundup Ready soybean or conventional soybean then a follow up burndown may be warranted. The options for a follow up treatment to remove this escaped horseweed would be paraquat, Liberty, Sharpen or Verdict. Δ
   DR. LARRY STECKEL: Extension Weed Scientist, University of Tennessee