Pendimethalin plus atrazine (1,120 2,240 g ai/ha) or metolachlor plus atrazine (2,170 1,790 g ai/ha) applied PRE over 2 yr controlled broadleaf signalgrass and itchgrass 78 to 88% 30 d after treatment (DAT). The imazethapyr plus imazapyr prepackaged mixture (PREMIX) applied PRE at 47 16 g ai/ha controlled these weeds no more than 35%. With pendimethalin, metolachlor plus atrazine, or atrazine PRE followed by (fb) imazethapyr plus imazapyr POST, broadleaf signalgrass was controlled 89 to 98% and itchgrass 76 to 83% 28 d after POST application. When only imazethapyr plus imazapyr was applied POST, broadleaf signalgrass control was 88% the first year, but only 64% the second year. Itchgrass was controlled 71% when imazethapyr plus imazapyr was applied alone POST, but control was nearly 86% when pendimethalin or nicosulfuron was applied POST with imazethapyr plus imazapyr. Consistently high corn yields were obtained when pendimethalin was applied POST with imazethapyr plus imazapyr, and these corn yields were greater than those following POST-only applications of imazethapyr plus imazapyr in 1 of 2 yr. When imazethapyr plus imazapyr was applied alone POST, corn yield was at least 1.3 times that when imazethapyr plus imazapyr was applied alone PRE. Weed control with imazethapyr plus imazapyr POST at 47 16 g/ha was not improved when ammonium sulfate was added with nonionionic surfactant or when methylated seed oil with or without ammonium sulfate or organosilicone adjuvants were used in the spray solution compared with using only nonionic surfactant in the spray solution. When imazethapyr plus imazapyr plus the various adjuvants was applied to weeds 5 to 8 cm tall, broadleaf signalgrass was controlled 93%, itchgrass 74 and 88%, and pitted morningglory 87 and 93% 28 DAT over 2 yr.
Nomenclature: Atrazine; imazapyr; imazethapyr; metolachlor; nicosulfuron; pendimethalin; broadleaf signalgrass, Brachiaria platyphylla (Griesb.) Nash #3 BRAPP; itchgrass, Rottboellia cochinchinensis (Lour.) W. D. Clayton # ROOEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; corn, Zea mays L. ‘Pioneer 3395 IR.’
Additional index words: Adjuvants, application timing, herbicide combinations, imidazolinone-resistant corn, tank mixture.
Abbreviations: DAT, days after treatment; EPOST, early postemergence; fb, followed by; IR, imidazolinone-resistant; LPOST, late postemergence; PREMIX, prepackaged mixture.