Control of Glyphosate Resistant Palmer Amaranth in Soybean.

Glyphosate resistant Palmer amaranth (Amaranthus palmeri) has been confirmed in 9 southern states; therefore, aggressive weed management programs are needed.  Herbicide efficacy experiments were established in 2009 and 2010 in a field heavily infested with Palmer amaranth to determine effective control programs in soybean.  In 2009, glyphosate applied at 0.84 kg a.e. ha^-1 at 1 week after planting (WAP), 0.84 kg a.e. ha^-1 at 3 WAP, and 1.68 kg a.e. ha^-1 at 5 WAP provided only 80% season-long control.  Glyphosate applied after preemergence herbicides improved control with glyphosate up to 90%.  In Liberty Link® soybean, glufosinate applied 0.45 kg ha^-1 at 1 and 3 WAP or applied at 0.45 kg ha^-1 following a preemergence herbicide provided greater than 95% control.  The most effective conventional weed control programs resulted in greater than 90% control of Palmer amaranth.  The 2010 data will be presented at the conference.