Another week and more reports and field visits to fields where Palmer amaranth is escaping glufosinate, glyphosate and dicamba.  These escapes range from relatively small pockets in fields to almost complete Palmer amaranth jail breaks across large portions of fields (Picture 1 and 2).

We have “been there and done that” with glyphosate and later PPO herbicides on how this plays out. Field visits this spring remind me of back in 2009 and 2010 where we reached a critical mass of glyphosate and PPO-resistant pigweed-infested fields. By 2011 most fields had some level of infestation of resistant pigweed and some were so bad they had to be disked up and replanted.

What is different this time is that goosegrass is also fairly prevalent in some of these fields as well (Picture 3).  Based on our latest goosegrass research in several counties, this is not surprising as glyphosate-resistant goosegrass is very prevalent across West Tennessee.  Clethodim at a full rate can still provide about 70 to 80% control which is borderline good enough but when dicamba or glufosinate are used in a tankmix with clethodim the control goes down dramatically.

In order to not repeat history let’s start planning weed control in these heavily infested fields now.  The plan should center around residual herbicides that minimize pigweed and grass emergence and then overlap those residual herbicides to keep them from coming up. This may be easier said than done, but we simply cannot rely on POST applications.