Acetolactate synthase-resistant and -susceptible corn (Zea mays) response to Imazethapyr, Imazaquin, Chlorimuron, and CGA-l52005

Field experiments were conducted from 1993 to 1995 to evaluate the response of ALS-resistant and ALS-susceptible corn to imazethapyr, imazaquin, chlorimuron, and CGA-152005 at label and twice label rates applied preplant incorporated (PPI) and postmergence (POST). The susceptible hybrid (P3245) and the resistant hybrid (P3245IR) grain yield were not different where weeds were removed by hand-weeding alone. Alachlor plus atrazine alone plus hand-weeding reduced grain yield by 5% compared to hand-weeding only. Imazethapyr applied PPI and POST reduced height of the susceptible hybrid 11 and 6%, respectively, averaged across imazethapyr rates. Imazaquin reduced the final height of the susceptible hybrid by 30 to 75% and reduced corn density by 62 to 78%. Chlorimuron applied PPI reduced final corn height of the susceptible hybrid by 26 to 36% and density by 27%. Chlorimuron applied PPI and imazaquin applied PPI and POST reduced grain yield of the susceptible hybrid. Imazethapyr did not reduce grain yield of the susceptible hybrid, regardless of application timing or rate. Imazethapyr, imazaquin, and chlorimuron did not reduce height, density, or grain yield of the resistant hybrid, regardless of application timing or rate, CGA-152005 applied PPI reduced grain yield of the susceptible and resistant hybrid. CGA-152005 applied POST did not reduce grain yield, regardless of hybrid or rate.