I have seen more canola growing around Pullman this year than I recall seeing before. There are probably a couple of things driving this increase. One is the sharp drop in chickpea and lentil prices and the other is Italian ryegrass control.
Italian ryegrass is the poster child for herbicide resistance in Eastern Washington. Frequent use of ACCase (Group 1) and ALS (Group 2) herbicides in our wheat-centric cropping systems has selected for biotypes that are resistant to most herbicides in these two groups. Growers in the high rainfall region, where Italian ryegrass is most problematic, are quickly running out of herbicide options to control Italian ryegrass and it is rapidly spreading throughout the region.
Roundup Ready canola provides growers with an opportunity to use glyphosate (Group 9) in the crop to assist in the control of Italian ryegrass. I am a big fan of crop rotation for the management of weeds; however, I wonder how many growers are using glyphosate as the only herbicide for Italian ryegrass control in their Roundup Ready canola?
I can think of no better way to quickly select for Italian ryegrass biotypes resistant to glyphosate than to rely solely on glyphosate for the control of Italian ryegrass. When growing Roundup Ready canola, glyphosate should be used in tandem with a Group 3 preemergence herbicide such as ethalfluralin (Sonalan) or trifluralin (Treflan). Alternatively, glyphosate could be applied with an ACCase herbicide such as clethodim (Select), quizalofop P-ethyl (Assure II), or sethoxydim (Poast), but only if the particular ACCase herbicide is still effective on the Italian ryegrass biotype that is being treated.
Glyphosate-resistant Italian ryegrass is present in orchards in the Pacific Northwest. We don’t want to select for it in our wheat production systems.
For questions or comments, contact Drew Lyon by phone at 509-335-2961 or via email drew.lyon@wsu.edu.