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Normally just Roundup’ is the worst possible answer you can hear when you ask an Ontario maize and soya bean grower what their herbicide programme is. The majority of corn and soya beans grown here in Ontario are genetically modified and with glyphosate tolerance. Today, there is a growing number of weeds that are actually resistant to glyphosate.
In my last article, I spoke about how septoria resistance is a major problem for the Irish wheat grower. If anything, weed resistance is an even greater problem here, as weed resistance spreads from the south of the province.
Roundup-ready
The first glyphosate-resistant or Roundup-ready crop in Canada was canola (oilseed rape) which was first introduced in 1996. Soya beans followed and Roundup-ready seed was available in 1997. Corn (maize) was the last crop to become glyphosate-resistant in the early 2000s.
This was a major change for farmers here – a herbicide that could essentially kill every weed except the crop itself. Once corn became Roundup-ready, a grower here could essentially use glyphosate as their only herbicide two years in a row if they were growing corn, soya beans and wheat in a three-year rotation. If they weren’t growing wheat, they could use glyphosate indefinitely.
Irish farmers will know at this point that it is dangerous to rely on just one mode of action as a means of control for either weeds or diseases. In a lot of cases, growers were adding in an additional mode of action, especially in corn, but there is much of the soya bean area that I work in sprayed with glyphosate only.
The introduction of glyphosate-resistant crops here provided growers with an excellent weed control too. However, they are now being asked to add other crops back into the rotation such as conventional corn, soya beans, wheat and even alfalfa.
Resistant weeds
There are actually 36 weeds worldwide that are resistant to glyphosate. Here in Ontario there are four – giant ragweed, Canada fleabane (also known as mares tail), common ragweed and waterhemp. Giant ragweed was the first glyphosate-resistant weed found in 2008, with waterhemp discovered in 2014.
There has been extensive research completed by Peter Sikkema from the University of Guelph tracking the development of glyphosate resistance and how that resistance has spread across the province. His research has shown that Canada fleabane is the biggest weed issue facing Ontario growers. It was first discovered as being glyphosate-resistant in 2010 in Essex county, the most southerly county in the province.
As you can see in Figure 1, by 2015 it had spread to more than 30 counties in the province. It is scary to think how this weed spread in just five years. The issue now isn’t just with glyphosate. In this time, Canada fleabane has become multiple resistant in 23 counties in the province. It is resistant to two modes of action, glyphosate and ALS inhibitors.
Canada fleabane is a hugely aggressive weed and produces very high seed numbers from just one plant. This is the main reason for its spreading through the province in such a short time. Peter Sikkema’s research has shown that Canada fleabane can cause up to 65% yield loss in Roundup-ready corn if not controlled effectively.
The good news is there are herbicide control options to control Canada fleabane in Roundup-ready corn, but not as many in soya beans. There are basically two options for weed control post-emergence in soya beans and now fleabane is resistant to both (glyphosate and ALS inhibitors). This has led to the introduction of Xtend soya beans for the 2017 growing season.
Xtend soya beans
In response to the growing issue of glyphosate-resistant weeds, Monsanto has introduced new genetically modified technology for soya beans. The Xtend system is resistant to both glyphosate and dicamba. It will be an excellent option to control multiple resistant Canada fleabane and will be available for the first time this season.
Monsanto has been working on this technology for some time and has bred some excellent varieties with this trait. The Xtend system will be essential for soya bean growers, especially for growers in the southern part of the province. In its first year, there has been a huge uptake of the new technology and Monsanto estimates that up to 50% of its soya bean seed sales this season will have the Xtend technology.
To put that trend in acre terms, over one million acres of soya beans grown here will have Xtend technology in 2017. The majority of these orders will be in the south, the birthplace of all glyphosate-resistant weeds in Ontario. The uptake in my area is much lower than this, but growers are aware of the technology and the likelihood is that in less than five years, all soya bean acres grown here will have this technology.
Stewardship
The build-up of glyphosate-resistant weeds isn’t just a chemical problem – it’s a chemical management problem. As we know too well, pesticide stewardship is part of what we do. When a new chemical comes to market, whether it be a fungicide or herbicide, the most important thing we have to do as farmers and agronomists is to ensure the longevity of that chemical by managing it properly.
Unfortunately, this isn’t always done, but chemical companies have got much better at ensuring that new chemistry is managed properly. The introduction of SDHIs to the Irish fungicide market is another example of where pesticide stewardship is needed. Nowadays, there is growing realisation that these very important actives should be used as little as possible and at more beneficial T2 timing.
The natural reaction to good new chemistry is to use it as much as possible. In some ways, Roundup-ready fell into this trap in Ontario and now the industry is reacting to that. The fact is that pesticide resistance is a global problem and we have to focus more than ever to put everything in place to stop the spread of resistance.
Pesticide stewardship, multiple modes of action and chemistry rotation is part of the solution, but we also have to look at more crop rotations and cultural tools as other forms of reducing the risk. I have certainly enjoyed my time working as an agronomist here in Ontario, but my time is coming to an end. I’m looking forward to moving home and the next challenge that brings.
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