Five Weeds to Watch for in Canola

Sally Krueger

May 24, 2018

Weed control is always a key part of farm management. Weeds left unabated compete with your crops for resources, eventually leading to unfulfilled yield potential at harvest. This is especially true in canolaproduction, with some reports saying that weed management plays an even bigger role in a canola crop’s success than fertilizer or seed genetics.

Here are five weeds to be on the lookout for in your canola crop this spring.


As they grow towards sunlight, cleavers grab on to canola plants and inhibit crop development. Their seeds are similar in size to canola seeds, so a wealth of cleavers in your harvest can lead to a downgrade in your crop. No.1 canola can include less than 1.0 percent of other seeds that are not readily separable. The limit is 1.5 percent for No.2 and 2.0 percent for No.3.

Pre-seed burnoff is the most effective way to control cleavers. Using an insufficient rate of burnoff can lead to fall cleavers that overwinter. If cleavers are particularly bad, a fall application of glyphosate followed by spring pre-seed burnoff can help reduce weed populations.


Canada thistle is incredibly competitive, and left unchecked, it can lead to significant yield loss in canola. Studies show that 20 Canada thistle shoots can reduce canola yield by 24 percent. Canada thistle spreads by both seeds (each plant producing up to 700 seeds per plant) and through creeping horizontal roots, causing it to often require a multi-year, integrated control strategy; pre-harvest glyphosate and clopyralid-containing herbicides can help provide control. 


A tough weed to kill, wild buckwheat can grow as high as 1 metre through the crop and has a fibrous root system that can chase water and nutrients up to 80 centimetres deep, making it significant competitor. This plant progresses through its growth stages quickly, so early control is essential, as it can produce 1,000 seeds per plant. Two herbicide passes may be required in fields with high wild buckwheat counts. This weed exhibits Group 2 resistance, so multiple modes of action are important in the tank mix.


Best controlled when it is small, kochia is well known for its prolific seed production—up to 15,000 seeds per plant—as well as its ability to shed spray droplets from its fuzzy leaves. It’s high level of genetic variability has allowed kochia to become resistant to various herbicide groups, most notoriously to glyphosate. Kochia tends to be more common in the southern Prairies, but has spread recently due to its ability to survive in moderate to high salinity soils.  


An aggressive competitor for nutrients, hemp-nettle germinates later in spring, when soil temperatures have increased. When this weed is left unchecked, yield losses can reach up to 25 percent in canola. This plant is easy to identify as a seedling due to its uniquely shaped cotyledon (the embryonic leaf that is one of the first leaves to appear from a germinating seed). Hemp-nettle has developed resistance to some Group 2 and Group 4 herbicides, but combinations including Group 6 and or Group 27 have been effective. Early application is key. 


Sally Krueger

May 24, 2018