Tolerance of Winter Canola (Brassica napus) Cultivars to Selected Residual Herbicides

Abstract

Winter canola planting continues to increase in Oklahoma and the Southern Great Plains due to the need for a winter broadleaf crop to rotate with winter wheat in order to expand weed control options. ALS-inhibiting herbicides are commonly used in winter wheat each year in this region. Several of these herbicides have rotational crop restrictions that do not permit seeding winter canola the following year. Field experiments were conducted from 2005 to 2007 and repeated from 2006 to 2008 at three sites to evaluate canola tolerance to ten selected ALS-enzyme inhibiting herbicides. Factors included herbicide treatment applied to wheat and canola cultivar seeded the following fall. The two canola cultivars seeded vary in response to ALS herbicides. The ten herbicides, all registered for use in wheat, were applied at 1x and 2x rates. Additional experiments were conducted to investigate the response of the same two canola cultivars to multiple rates (one-half to five times the labeled rate) of chlorsulfuron + metsulfuron. Application of ALS-inhibiting herbicides to wheat seeded in December caused visible stunting and chlorosis to canola seeded the following fall at two sites one year and no sites the other year. However, canola yield was not reduced by any herbicide treatment applied to any experiment either year. The data suggest that winter canola can be grown with a much shorter rotational interval than stated on some product labels.