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Cover crops and tillage for glyphosate resistant Canada fleabane management

Principal Investigator

François Tardif, Clarence Swanton and Mike Cowbrough*

Research Institution

University of Guelph / Ontario Ministry of Agriculture and Rural Affairs (OMAFRA)*


May 2018 – October 2019


  • Understand the influence of cereal rye cover crop and fall tillage on the population of biology of fleabane as to optimise fleabane control.


  • The determination of the best timing and intensity for light fall tillage with or without cereal rye cover crop will allow farmers to optimise management of glyphosate resistant Canada fleabane in soybeans and reduce the requirement for pre-emergence or in-crop treatments the following spring.

Scientific Summary

Glyphosate resistant Canada fleabane is one of the most important issues facing growers in Ontario. This weed is very difficult to manage in soybeans and there are limited options to control it with herbicides. Some pre-emergence options exist but can be unreliable and new post-emergence technologies such as Xtend and Enlist, while effective, are not appealing to all growers. Tillage has been promoted by many as an effective way to control fleabane, but there is a lack of reliable data on this. In addition, heavy tillage is discouraged, and the efficacy of lighter tillage is still unknown. During preliminary trials, we have observed that light fall tillage is very effective at reducing fleabane density, but plants that survived that treatment grew taller the following spring, making them more difficult to control with herbicides. That preliminary trial site had an estimated 3.5 million fleabane seeds per acre in the soil. Yet there were no seedlings established where rye had been planted as a cover crop in the previous fall, which was completely unexpected. The mechanism underlying this very unique observation is not known. Although pre- and post-harvest tillage, use of cover crops and herbicide selection all play a role in the management of glyphosate resistant Canada fleabane, Ontario grain farmers have still experienced late seedling recruitment of the weed that cannot be addressed by any of those three strategies.

Through this project, researchers plan to examine the effect of rye cover crop and tillage on the population dynamics of Canada fleabane. They will be planting rye cover crop with and without tillage and monitor the seed bank and population of seedlings in the fall and spring. This will allow researchers to determine the best cultural/physical control methods to reduce the impact of this weed and provide recommendations to growers managing this difficult weed.

External Funding Partners

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.

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