In western Canada, more money is spent on wild oat herbicides than on any
other weed species, and wild oat resistance to herbicides is the most
widespread resistance issue. A direct-seeded field experiment was conducted
from 2010 to 2014 at eight Canadian sites to determine crop life cycle, crop
species, crop seeding rate, crop usage, and herbicide rate combination
effects on wild oat management and canola yield. Combining 2× seeding rates
of early-cut barley silage with 2× seeding rates of winter cereals and
excluding wild oat herbicides for 3 of 5 yr (2011 to 2013) often led to
similar wild oat density, aboveground wild oat biomass, wild oat seed
density in the soil, and canola yield as a repeated canola–wheat rotation
under a full wild oat herbicide rate regime. Wild oat was similarly well
managed after 3 yr of perennial alfalfa without wild oat herbicides.
Forgoing wild oat herbicides in only 2 of 5 yr from exclusively summer
annual crop rotations resulted in higher wild oat density, biomass, and seed
banks. Management systems that effectively combine diverse and optimal
cultural practices against weeds, and limit herbicide use, reduce selection
pressure for weed resistance to herbicides and prolong the utility of
threatened herbicide tools.