Effects of Imazamox Application Timing and Rate on Imazamox-Resistant Winter Wheat in the Pacific Northwest.
Arron Carter1, Jennifer Hansen1, Thomas Koehler2, and Robert Zemetra1. (1) Univ of Idaho, Dept of PSES, P.O. Box 442339, Moscow, ID 83843, (2) Univ of Idaho, Dept of PSES, P.O. Box 442339, Moscow, ID 83843
Annual grass weeds are a major problem in winter wheat (Triticum aestivum L.) fields in the Pacific Northwest (PNW). Control of these weeds can be enhanced when imazamox herbicide is applied to imazamox-resistant winter wheat cultivars, which have been rapidly adopted by wheat growers. However, limited information is available on the affect of imazamox application rate and timing on crop injury and agronomic traits of wheat cultivars with different genetic backgrounds. Experiments were conducted near Moscow and Genesee, ID during the 2003-2004 and 2004-2005 growing seasons to evaluate the effect of imazamox application time and rate on four resistant winter wheat cultivars and seven resistant breeding lines. Wheat plants were treated at the 3-5 leaf stage and the late tiller stage with 45 g ai/ha and 90 g ai/ha of imazamox. Visible crop injury was evaluated periodically from 14 to 35 days after treatment (DAT). Heading date, plant height, grain yield, test weight, and end-use grain quality were determined. There was a significant cultivar by treatment interaction for visible crop injury at 21 DAT, and for plant height and grain yield. Although cultivars and breeding lines responded differently to imazamox treatment, entries from the ‘Lambert’ background consistently showed the lowest levels (3-8%) of crop injury, and no reductions in plant height or grain yield following imazamox application. Orthogonal contrasts of visible crop injury at 21 DAT showed that the 2X imazamox rate injured wheat 12%, while injury was 7% at the 1X rate. The 2X rate of imazamox reduced plant height 1%, grain yield 8%, test weight 1%, and percent flour yield 1% compared to the untreated control. All other traits were not affected by application of imazamox. Imazamox application timing minimally affected crop injury, and did not affect agronomic or end-use quality traits.