2021-22 New Research Commitments
Manitoba Crop Alliance entered into funding agreements for several new research projects in the 2021-22 fiscal year. Dow...
While the winter annual growth habit and rapid spring growth of winter wheat means it can effectively out-compete many weeds, some considerations to weed control should still be made. Herbicides are an important tool, but a variety of other practices can also be implemented to manage weeds in winter wheat crops.
Integrated weed management
There are several integrated weed management practices available to famers that may help encourage the competitive nature of winter wheat:
Herbicide options
Despite using best management practices, herbicides may still be necessary in the fall or spring. If winterkill occurs, the competitiveness of the crop will be impacted and more intensive weed management may be needed. Winter annual weeds, such as stinkweed, shepherd’s purse, downy brome and Japanese brome, can be particularly challenging in winter wheat.
When applying herbicides, be aware of the maximum winter wheat growth stage on the herbicide label to avoid damage to the crop. Application of some herbicides when the crop is stressed due to cold temperatures, drought or frost can also increase the risk of crop damage and will reduce the efficacy of the herbicide. There are several opportunities for herbicide application in winter wheat:
Control of annual bromes
Winter annual grasses, such as downy and Japanese brome, can be very competitive in winter wheat and have the potential to cause significant yield losses if they remain uncontrolled.
When choosing an herbicide for control of bromes, it is important to be aware of which species is present, as downy brome is more challenging to control than Japanese brome and some herbicide options may not control both species. For identification characteristics of Japanese and downy brome, the government of Saskatchewan has a helpful guide here.
Limited in-crop options exist for the control of bromes in winter wheat, but several chemistries are available. In a study performed in Alberta, pyroxsulam-containing herbicides (Simplicity™) applied in the fall post-emergence provided greater than 70 per cent and 90 per cent control of downy and Japanese brome, respectively, while flucarbazone and thiencarbazone provided control that was slightly less efficient5. Consult the Guide to Field Crop Protection for a complete list of herbicide options.
Herbicide resistance is also an emerging issue for downy brome. Plants with resistance to Group 1 and Group 2 herbicides have been found across the western United States, and downy brome with resistance to glyphosate was found in Alberta in 2021. To prevent the development of herbicide resistance, consider using tank mixes and rotating herbicide groups/site of action, as well as maintaining a diverse crop rotation.
In winter wheat, as in all crops, weed control must include a variety of management practices to ensure the crop is healthy and productive, while reducing the risk of developing herbicide-resistant weeds. Maximizing the competitive nature of winter wheat, combined with wise use of herbicides, will allow for an effective weed management plan.
Additional resources
Manitoba Agriculture:
Guide to Field Crop Protection
Integrated Weed Management – Making it Work on Your Farm
Winter Wheat – Production and Management
Western Winter Wheat Initiative:
Invasive Species Council of Manitoba:
Government of Saskatchewan:
References
1. Blackshaw, R. E., Molnar, L. J. & Larney, F. J. Fertilizer, manure and compost effects on weed growth and competition with winter wheat in western Canada. Crop Prot. 24, 971–980 (2005).
2. Beres, B. L. et al. Influence of N fertilization method on weed growth, grain yield and grain protein concentration in no-till winter wheat. Can. J. Plant Sci. 90, 637–644 (2010).
3. Beres, B. L. et al. A sustainable management package to improve winter wheat production and competition with weeds. Agron. J. 102, 649–657 (2010).
4. Beres, B. L. et al. Weed-competitive ability of spring and winter cereals in the northern Great Plains. Weed Technol. 24, 108–116 (2010).
5. Johnson, E. N. et al. Pyroxasulfone is effective for management of Bromus spp. in winter wheat in Western Canada. Weed Technol. 32, 739–748 (2018).