Managing Glyphosate Resistant Canada Fleabane with Cover Crops and Tillage

My colleague Dr. Clarence Swanton (University of Guelph) used to say that based on research he did in the 1980’s, one should not expect to control weeds with cover crops. Their utility was in preventing soil erosion and improving soil health but not in significantly reducing weed populations. However, Dr. Swanton has had to re-think his long held position on cover crops and weed control given recent observations from on-farm research trials where fall seeded cereal rye has reduced glyphosate resistant Canada fleabane populations.

University of Guelph graduate student Ted Vanhie, under the supervision of both Swanton and Dr. François Tardif are looking at an integrated approach to the control of glyphosate resistant Canada fleabane using tillage, herbicides and fall seeded cereal rye. The concept being that frost seeding fall rye ahead of soybeans could significantly reduce populations of this weed and improve herbicide control. Below are observations Mr. Vanhie has made during the spring of 2018.

  1. Fall tillage followed by planting cereal rye resulted in the best control of glyphosate resistant Canada fleabane in the absence of herbicides. (Figure 1)
  2. Although glyphosate resistant Canada fleabane was still found in no-till fall seeded cereal rye, there were fewer and smaller plants compared to where no cereal rye was established and no fall tillage operation performed. (Figure 2 and 3).
  3. Control of Canada fleabane with herbicides was improved in no-till plots where cereal rye was established (Figure 4 – preliminary data from Ted Vanhie)
  4. Cereal rye at 50-60 lbs/acre provides little ground cover and shading. It is speculated that there is allelopathy inhibiting recruitment of glyphosate resistant Canada fleabane (Figure 5). Further experiments will test this hypothesis.
Figure 1: An overhead look at the level of control that cereal rye has provided when it was seeded the previous fall (mid-November) at 60 lbs/acre (left) compared to no cereal rye planted (right).


Figure 2: Height of glyphosate resistant Canada fleabane within fall seeded cereal rye.


Figure 3: Height of glyphosate resistant Canada fleabane in the absence of fall seeded cereal rye.


Figure 4: Visual control of Canada fleabane with Eragon LQ (59 mL/ac) + Merge adjuvant (400 mL/ac) applied in three different tillage systems (no till, light tillage, aggressive tillage) and in the presence or absence of a fall seeded cereal rye cover crop (60 lbs/ac).


Figure 5: The recruitment of glyphosate resistant Canada fleabane appeared to stop within 10-15 cm of the outside row of cereal rye, prompting the speculation that differences in weed populations amongst treatments may be due to allelopathy.


Project Funding Acknowledgement:

 This project was funded in part through the Canadian Agricultural Partnership (the Partnership), a federal-provincial-territorial initiative. The Agricultural Adaptation Council assists in the delivery of the Partnership in Ontario.

This project was also funded in part through Grain Farmers of Ontario.