Agronomy •  2022-12-19

Controlling Canada Fleabane with a program approach

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There was a time when Canada fleabane was just an annoying roadside weed. Not any more. The first documented case of glyphosate-resistant Canada fleabane in Ontario was in 2010 and, by 2016, it was found in at least 29 more counties1. Today, Canada fleabane is the number one glyphosate-resistant weed in Ontario, plus there are now biotypes resistant to Group 2 herbicides, Groups 9 and 2 together, and Group 22 herbicides.2

For those growing Enlist E3 soybeans, the program approach employs a Canada fleabane control strategy that puts multiple-mode-of-action (MMOA) herbicides at the centre. For both pre- and post-emergence applications, it’s a plan based on maintaining proper herbicide stewardship without compromising weed control.

The problem: Canada fleabane is a very competitive summer and winter annual that germinates almost all year round, which means it exists at various growth stages throughout the crop, throughout the growing season. One plant can produce up to 200,000 seeds. The seeds themselves are very small – only one to two millimeters – and attached to a pappus for easy dispersal by wind over very long distances.

Most populations of Canada fleabane likely carry resistance to both glyphosate (Group 9) and cloransulam (Group 2), while resistance to paraquat (Group 22) is slightly less frequent. This situation means that herbicide options are limited for soybean growers, and careful decisions have to be made to preserve the ones that are left.

Controlling Canada fleabane with the Enlist weed control system: A solid Canada fleabane herbicide program starts with good scouting and early spraying. Because Canada fleabane germinates almost all year round, early control in the spring is critical for strong soybean stand establishment. This is where pre-emergent, residual and MMOA herbicides are key.

Soybean trait and herbicide technology have an important role to play when it comes to managing resistant Canada fleabane, but these tools must be used responsibly in order to maintain their efficacy for as long as possible. Proper crop and herbicide group rotations, scouting, maintaining good field records and accurately following label instructions are all important to this effort.

The Enlist weed control system is comprised of Enlist E3 soybean varieties that are tolerant of 2,4-D (Group 4) and glufosinate (Group 10), and two Enlist herbicide options:

  • Enlist Duo herbicide a convenient proprietary blend of 2,4-D choline (Group 4 and 9) and glyphosate.
  • Enlist 1 herbicide a stand-alone 2,4-D choline formulation that can be tank-mixed with Liberty® 200 SN (Group 10) or glyphosate.

Both herbicides come with Colex-D technology for near-zero volatility and low drift so it stays where it’s sprayed.

The program approach: This is a two-pass system for Enlist E3 soybeans that pairs the Enlist herbicides along with Canopy PRO and Liberty 200 SN herbicides to deliver MMOA control of Canada fleabane.

  1. Pre-emergence residual herbicide: Apply a tank mix of Enlist Duo (Group 4 and 9) and Canopy PRO (Group 2 and 5) at pre-emergence. Again, because Canada fleabane is constantly germinating, the residual activity helps to keep new weeds at bay as the crop establishes. Plus, this tank mix offers four modes of action, including a Group 4 and a Group 5, against Canada fleabane.
  2. Post-emergence field maintenance. To keep fields clean, apply a post-emergence tank mix of Enlist 1 (Group 4) with Liberty 200 SN (Group 10). As of yet, Canada fleabane has no known resistance to Group 4 or Group 10 herbicides, so this is an effective tank mix to keep weed competition in check as the crop matures.

Glyphosate-resistant Canada fleabane is a critical problem for soybean growers, not only because of its herbicide resistance, but also because its wide window of emergence makes staying on top of new flushes that much more difficult. When mixed with Liberty 200 SN, Enlist herbicides can be applied right up to the beginning of flowering (R1), giving growers the ability to take care of late-emerging Canada fleabane and protect yield.

Key takeaways:

  • Two passes may be necessary. Canada fleabane can overwhelm a crop if not dealt with early. While early weed removal is critical, effective management may require a second, post-emergence herbicide application to control other late emerging weeds and protect yield and quality
  • MMOA is key. The ability to mix with Liberty 200 SN expands the MMOA offering –this program approach provides a total of five modes of action against weeds in soybeans, three of which are specifically effective against glyphosate-resistant Canada fleabane.
  • Practice good stewardship. Keep in mind that many populations of Canada fleabane are resistant to more than just glyphosate. If you grow soybeans, pay close attention to the modes of action you use, rotate them, and use MMOA whenever possible. This is the only way to preserve herbicide efficacy for as long as possible.


1Canadian Journal of Plant Science, Vol. 99, Number 1, January 2019. Glyphosate-resistant Canada fleabane in Ontario with multiple effective modes-of-action in glyphosate/dicamba-resistant soybean.,GR%20Canada%20fleabane%20in%20soybean.

2OMAFRA, Ontario weeds: Canada fleabane web page.