Published online by Cambridge University Press: 12 June 2017
Imazethapyr dose response curves were developed under laboratory and field conditions with the imazethapyr-resistant and -susceptible corn hybrids Pioneer 3180IR, IR denoting a hybrid homozygous for the XA17 gene conferring resistance to imazethapyr, and normal Pioneer 3180, respectively, and their F1 progeny to establish methods of measuring the presence of the XA17 gene and quantifying its impact. At two field locations, absorption of photosynthetically active radiation was a sensitive index of corn injury caused by imazethapyr. Imazethapyr, at 35 g/ha (one half the labeled rate), reduced absorption of photosynthetically active radiation in Pioneer 3180 by 8.3% at 1 wk after treatment. Plant height also was a sensitive index of injury. The minimum rate at which imazethapyr injury was detected in the Pioneer 3180IR/Pioneer 3180 F1 hybrid differed with location. Pioneer 3180IR was not injured by 280 g/ha of imazethapyr. The Pioneer 3180IR/3180 F1 hybrid was injured slightly by imazethapyr at 140 g/ha, but recovered within 5 wk after treatment, and grain yield was not reduced by 280 g/ha of imazethapyr. A seedling assay reliably detected differences between progeny of Pioneer 3180IR and Pioneer 3180IR/3180 F1.