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