Palmer Amaranth (Amaranthus palmeri) Control and Grain Sorghum (Sorghum bicolor) Injury with Pyrasulfotole plus Bromoxynil and Tank Mixtures

Field studies were conducted in 2009 and 2010 to determine control of Palmer amaranth and crop injury resulting from a postemergence (POST) premix application of pyrasulfotole + bromoxynil and various tank‐mix partners. The objectives were to (i) determine the effects of different pyrasulfotole + bromoxynil rates and tank‐mix partners applied at early and mid‐POST (EPOST and MPOST) on Palmer amaranth control; (ii) evaluate weed control following application at different Palmer amaranth sizes; and (iii) assess sorghum injury and yield as affected by herbicides applied at the 4‐leaf, 10‐leaf, and boot stages. At both EPOST and MPOST, pyrasulfotole + bromoxynil + atrazine alone or mixed with 2,4‐D or dicamba consistently provided better Palmer amaranth control (>98% at EPOST and >90% at MPOST) than bromoxynil + atrazine (94% at EPOST and 58% at MPOST). At EPOST, control of Palmer amaranth by pyrasulfotole + bromoxynil alone varied with year, but the control was 100% at 42 days after treatment (DAT) when pyrasulfotole + bromoxynil was tank‐mixed with atrazine at 0.50 lb a.i./acre or dicamba at 0.20 lb a.i./acre. Pyrasulfotole + bromoxynil at more than 0.02 + 0.14 lb a.i./acre plus atrazine at 0.50 lb a.i./acre provided 100% control at 42 DAT when Palmer amaranth was less than 9 inches tall. In controlling 15‐ to 18‐inch‐tall Palmer amaranth, the efficacy of pyrasulfotole + bromoxynil + atrazine ranged from 83% to 99%. Pyrasulfotole + bromoxynil + atrazine resulted in up to 28% leaf burn at 3 DAT when applied to 4‐leaf sorghum, but plants completely recovered from the injury within 28 DAT. Addition of dicamba to pyrasulfotole + bromoxynil + atrazine tended to reduce sorghum injury. However, application of pyrasulfotole + bromoxynil + atrazine + dicamba at the boot stage reduced sorghum grain yields up to 37%.