Agronomy •  2022-02-14

Dealing with Canada fleabane in soybeans requires a good plan

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brevant soybean rows

Here is a sobering statistic: the first documented citing of glyphosate-resistant Canada fleabane occurred in 2010. That year, it was identified in eight fields located in one county of Ontario. By 2015, a mere five years later, glyphosate-resistant Canada fleabane was found in 30 counties throughout Ontario.1

That rapid spread is proof of Canada fleabane’s most potent survival skills: the ability to travel far and the capacity to grow just about anywhere. Today, with a number of resistant biotypes growing in Ontario and Quebec, including some with multiple-resistance, soybean farmers have put resistant Canada fleabane in the number one spot when it comes to weed management issues.

So what can be done? It helps to have a plan to tackle this weed and that starts by understanding the plant itself – how it grows, how it disperses and when it’s most vulnerable. Second, develop an integrated management plan that includes cultural controls as well as chemical ones. Third, ensure your herbicide plan uses multiple modes of action and a have crop plan that supports the herbicide plan.

Canada fleabane: know how and when it grows

Canada fleabane prefers no-till environments and an adult plant can produce about 200,000 seeds. Surprisingly, even a small adult plant (less than 1.5 metres high) can produce somewhere around 2,000 seeds.

These seeds are very small (1-2 mm), nearly transparent and can be carried long distances on the wind using a pappus, or little parachute, similar to how dandelion seeds are dispersed. When conditions are right, seeds can be blown as far as 500 kilometres from the parent plant, but the vast majority land within 100 metres.2

Canada fleabane can behave like a winter or summer annual, depending on when a seed decides to germinate. By far, the majority of them germinate from mid-summer to late-fall, developing rosettes for overwintering. A smaller number of seeds germinate in the spring, skip the rosette stage, and go straight into bolting and flower development. This ability to switch between summer and winter means Canada fleabane emerges almost year-round with January being the only month it seems to take a break.3

Building an integrated weed management plan

As with any effective weed control program, an integrated approach that uses tillage, cover crops and herbicides is the most successful way to limit Canada fleabane.

Tillage: Because the seeds are so small and do not remain viable in the soil much beyond three years, tillage can be an effective tool in the battle against Canada fleabane. But there are limitations.

Research from Ontario shows that burying seed 6 cm deep eliminates germination altogether, while burying it only 1 cm deep can reduce germination by 90 per cent. While small Canada fleabane seedlings are also susceptible to tillage, bear in mind that even tiny rosettes and seedlings can hold on to their root soil and survive a tillage operation. 4

And last, while tillage can be a useful tool, it’s important to keep soil conservation in mind. Too-deep or too-aggressive tillage can cause more harm than good.

Cover crops: Not surprisingly, Canada fleabane does best in low-disturbance, low-competition environments. So where tillage interferes with seeds and seedlings, cover crops can offer a degree of competition to constrain fleabane emergence in the late summer and fall.2

Herbicides: The safest thing to assume is that, if you see Canada fleabane, it’s likely resistant to both glyphosate (Group 9) and cloransulam (Group 2), with a possibility of also being resistant to paraquat (Group 22).

A good herbicide regimen should include early application (pre-seed or pre-emergent) to control overwintered and early-emerging Canada fleabane seedlings, a fall burndown to control fleabane rosettes preparing for winter, and adopting a multi-mode of action (MMOA) herbicide program to address the resistance issues.

Herbicide and variety choices that target Canada fleabane

The Enlist weed control system with Enlist E3 soybeans is a valuable tool in the fight against Canada fleabane. This soybean production system includes herbicides that offer three different modes of action so you can take on glyphosate-resistant weeds, plus the latest in soybean technology, to get the most out of those herbicides without sacrificing yield.

First, the herbicides. Since early control of fleabane is key to overall success, start your MMOA approach off with Canopy PRO herbicide and Elevore herbicide with Arylex active.

  • Canopy PRO contains both Group 2 and Group 5 active ingredients that can be applied either pre-plant or pre-emergence for effective early-season knockdown of Canada fleabane, as well as broad-spectrum residual activity to help keep weeds in check as your soybeans establish.
  • Elevore with Arylex active is a Group 4, pre-plant burndown herbicide that’s highly effective against broadleaf weeds, including glyphosate-resistant Canada fleabane and Group 2 resistant weeds.

The Enlist weed control system gives you two post-emergent herbicides to choose from, both of which use different modes of action against resistant Canada fleabane:

  • Enlist Duo™ is a proprietary blend of 2,4-D choline (Group 4 and 9) and glyphosate for control of resistant fleabane populations as well as non-glyphosate resistant weeds.
  • Enlist 1 is a stand-alone 2,4-D choline formulation (Group 4) that can be tank-mixed with Liberty 200 SN, a Group 10 glufosinate - two modes of action that are still effective against glyphosate-resistant Canada fleabane.

Both herbicides feature Colex-D technology for near-zero volatility and minimized potential for physical drift – it stays where it’s sprayed.

As the seed component of the Enlist weed control system, Brevant® seeds Enlist E3 soybeans give you some flexibility to manage resistant Canada fleabane while delivering the soybean yield and quality you’re looking for.

Enlist E3 soybeans are tolerant to 2,4-D, glyphosate and glufosinate, and robustly tolerant to the Colex-D technology found in Enlist herbicides, so you can apply them right up to the R2 stage if necessary, giving you more weed control options.

Plus, Enlist E3 soybeans are simply better beans. Offering the latest in soybean technology, there is a wide range of Enlist E3 soybean varieties to choose from with maturities to suit all growing regions. These are high-yielding genetics that come with great agronomic packages, including excellent disease resistance.

A multi-pronged approach to Canada fleabane

Effective management of glyphosate-resistant Canada fleabane in soybeans relies on many factors – vigilance when it comes to weed presence and behaviour, plus using all the cultural and chemical tools at your disposal. Canada fleabane is most definitely a challenge, but it is one we can meet.




1 Glyphosate-resistant weeds in Ontario, by Peter Sikkema, Top Crop Manager, September 2018.

2 Limit corn and soybean losses due to GR Canada fleabane, by Madeleine Baerg, Top Crop Manager, March 2018.

3 Controlling Canada fleabane in soybean, by Julienne Isaacs, Top Crop Manager, March 2018.

4 Field Crop News, 2017 ERICA PWB 2017