Timing of post-emergent weed control in Canola

Producers are always looking for opportunities to increase yield potential of their crop without increasing production costs. Proper timing of the post-emergent herbicide applications in canola is one of those opportunities. The cost of the application does not increase but the resulting yield can increase significantly if the timing is right.

Early weed control in canola allows for better emergence of the canola and less competition for moisture and nutrients with the weeds. Herbicide timing trials have shown that herbicide applications at the 1 to 2 leaf stage provided an average yield increase of 3 bushels per acre compared to waiting until the 3 to 4 leaf stage. The yield advantage from early weed removal increases to 7 bushels per acre when comparing the 1 to 2 leaf stage and the 6 to 7 leaf stage.

Weeds emerging after the 4 leaf stage of the crop are normally weaker and not as competitive with the crop. Waiting for these weeds to emerge prior to herbicide application does not usually translate into yield.

Late applications are seldom warranted. There may be exceptions where a late application is warranted because of the type of weed that is present. Two weeds that fit into this category would be cleavers and wild buckwheat that affect either crop quality or ease of harvest. Challenges such as advanced growth stage of the weeds and canopy closure that reduces effectiveness of the herbicide in late applications should be considered when planning late applications.

Early weed control provides the highest yield potential without increasing costs and should be what canola producers strive to achieve.

For more information on post-emergent weed control in canola contact a Crops Extension Specialist at your closest Regional Services Office or call the Agriculture Knowledge Centre at 1-866-457-2377.