Ontario farmers warned about the growing presence of herbicide resistant weeds

Friday, April 4, 2014

Experts say that three glyphosate-resistant varieties have already established themselves in the province and more may be coming. Industry is developing some solutions, but farmers may have to come up with their own strategies, too

by MARY BAXTER and MATT MCINTOSH

François Tardif jokes about the different ways "weed researcher" can be interpreted and how, when he goes to the United States, he's careful to describe himself as an agronomist.

There's appreciative laughter from the farmers who've jammed into a London banquet hall to hear the University of Guelph plant agriculture associate professor and several others speak during the annual Innovative Farmers Association of Ontario conference.  

Nevertheless, Tardif's message to farmers attending the February conference was serious. He, as well as another University of Guelph professor and an Ontario Ministry of Agriculture and Food extension expert, are warning farmers about the growing presence of herbicide resistant weeds in Ontario farm fields. They say farmers will have to be proactive and perhaps even innovative in order to protect their crops from negative impacts.

Herbicides are classified into several groups based on their mode of action, or how they kill plants. That means, for example, that a weed which is immune from herbicides which disrupt photosynthesis may not be immune from one that inhibits amino-acid production.

Recently, concern has mostly centred on the increasing resistance to the popular and widely used glyphosate. According to the International Survey of Herbicide Resistant Weeds, there are now nearly 30 glyphosate-resistant weed varieties. Three of these varieties have established themselves in Ontario: glyphosate-resistant giant ragweed, first reported in 2008; glyphosate-resistant Canada fleabane, confirmed in 2010; and, confirmed in 2012, glyphosate-resistant common ragweed.

What is also of concern is that some weeds are developing resistance to different modes of action. Of the last round of surveys of Canada fleabane, 12 per cent of the samples that tested positive for glyphosate resistance also indicated resistance to cloransulam-methyl (the active ingredient in the Group 2 herbicide First Rate), as well as some other Group 2 herbicides.

Right now, finding an alternative herbicide here in Ontario is straightforward, says Tardif. And "globally, in terms of resistance in Ontario, we're pretty good." But challenges with herbicide resistant weeds in other countries suggest that it could eventually pose a significant problem here, too. For instance, in the southern United States, glyphosate-resistant palmer pigweed is such a problem that farmers have resorted to sending out crews to chop out the weeds.

(Tardif notes that this weed is moving north. According to a Michigan State University extension publication, the weed was found in southwest Michigan in 2010. The weed's Michigan presence appears to be localized, the publication notes.)

Industry is coming up with solutions, and hopefully the technologies will combat the glyphosate resistance problem, Tardif says. But will these solutions simply present new problems? "Are we going to get resistance to new technologies trying to solve the glyphosate issue?" he asks.

As a precaution, Tardif recommends using three or four competing technologies in rotation. Mix it up as much as possible, he advises, although he acknowledges farmers will likely experience pressure from herbicide manufacturers to stick with one product.

Peter Sikkema, associate professor of field crop weed management at the University of Guelph's Ridgetown campus, advises farmers to incorporate other strategies as well to help shield their crop from the growing problem, such as rotating crops whenever possible, planting crops with different resistance traits, tillage and using different herbicides.

Mike Cowbrough, a weed specialist at the Ministry of Agriculture and Food, notes that herbicide resistant crops are usually meant to work with brand-specific herbicides, and weeds will continue to develop tolerances naturally.

"They might be helpful in the short term, but 10 years from now we will have an even more significant problem . . . weeds will continue developing multiple herbicide resistances," he says.

Cowbrough explains that many of the weeds showing herbicide resistance have their origin in soybean fields. This is because, when compared to something like corn, there are generally fewer weed control products available for farmers to use. Combine that with consistent exposure in a soy-heavy area like Essex County, and the reality, he says, speaks for itself.

"It's as if you have a headache and Advil and Tylenol just stop working," he says.

Ultimately, as weed resistance becomes a greater problem, farmers will have three choices to cope, says Tardif. Give up farming; wait for a government solution ("Oh yeah," he quips. "Eventually things will happen and we'll get a report."); or decide to figure it out for themselves.

That's what farmers in Australia, who are dealing in some places with annual rye grass and wild radish that now resist several modes of action, have done by deciding to target the weed seed bank in soil at harvest, he says. They have introduced a chute at the back of combines so the crop and weed residue forms windrows. The windrows are then destroyed through controlled fires.

"Doing that for a few years, Australian farmers have been able to reduce the weed populations" to the point where "even if the post-emergence herbicide isn't working well, they still get a decent crop on that," Tardif says. However, the loss of organic matter is a drawback.

Recently, Western Australian farmer Ray Harrington came up with yet another approach – the Harrington seed destructor unit, which is attached behind a combine. The unit destroys seeds by pulverizing crop residue before releasing it. A 2011 study indicates its efficiency in destroying weed seed ranges from 93 to 99 per cent, depending on seed type.

The unit has been commercialized but is expensive and takes a lot of power, Tardif notes. Nevertheless, just as cell phones used to be really large and are now tiny and multifunctional, the mechanical destruction of weed seeds could also be refined over time. Even now, a smaller model is being developed that can fit right inside a combine to separate weed seeds and destroy them.

Agriculture and Agri-Food Canada is acquiring a unit this year and "so hopefully we will be able to demo a Harrington seed destructor in Ontario this summer," Tardif says.

Back in Ontario, Tardif points to an initiative that he, Cowbrough and several other researchers are involved with. They've entitled it "Fight the Light," because it's looking at different ways to discourage weed growth by using the shading effect of crop canopy.

If light does not reach the weed, Tardif explains, it won't germinate.

One of the initiative's projects is a study exploring how to close a soybean canopy as quickly as possible and what the effects are of the shade the canopy produces on weed germination. The study began in 2013 on two sites and explores the question of which of three factors contributes the most to quicker canopy closure: fertilizer early on in the growth season, cultivar type or planting density. The study is continuing through 2015.

Another project explores the performance of cover crops in terms of weed control in a typical rotation involving corn, soybeans and wheat. It will run for at least two years, Tardif notes. The initiative is part of the research agreement between the Ontario agriculture ministry and the University of Guelph and has additional funding from the Grain Farmers of Ontario and Pioneer.

Ultimately, the goal of adding different methods of weed control is not to eliminate the use of herbicides, but instead to ease pressure on that method. "The way the system works now, the herbicide has to do 100 per cent of the weed control work and sometimes it's too much. That's why we get weed resistance problems. It's simplified the system too much. So let's try to get some more diversity in the system in a way that's still accessible to farmers," Tardif says. BF

Vary your herbicides, researcher advises
In order to proactively manage weeds with herbicide, Peter Sikkema, associate professor of field crop weed management at the University of Guelph's Ridgetown campus, says farmers need to avoid using the same product year after year.

"All farmers need to adopt strategies to minimize the selection intensity of herbicide resistant weeds," he says. "Herbicide rotation is very important; there are a lot of options farmers could consider."

Sikkema says two new products will soon provide producers with more options when it comes to spraying, at least in the short term:

• Monsanto's Roundup Ready 2 Xtend brand of soybeans is resistant to glyphosate herbicides and Dicamba (otherwise known as Banvel)
• Dow AgriSciences' Enlist variety of soybeans and corn can tolerate glyphosate herbicides, 2,4-D and Liberty

Both varieties should be available to farmers very soon, he says. BF