Your Reading List

Sharing the lessons learned on dicamba in soybeans

Misconceptions about the power of the technology remain, in spite of some harsh in-field realities

When Xtend soybeans were showcased at the 2015 Canada Outdoor Farm Show, there was great fanfare but also a considerable amount of caution accompanying the technology’s unveiling. Yes, it was the next in a series of herbicide-tolerant technologies, launched at a time of growing concern over glyphosate-tolerant weed species. It was believed that the newer formulation of dicamba combined with glyphosate would lead to greater suppression of tough-to-manage weeds, including common and giant ragweed and Canada fleabane.

The Canadian registration of Xtendimax and Engenia for use in the Xtend soybean system gave Canadian growers a leg up on their cousins in the U.S., where neither product had been registered in time for the 2016 growing season.

Related Articles

That missed deadline had disastrous results for growers across the U.S., who were left without products specifically formulated for the Xtend system, resulting in damaged crops, lower yields and lawsuits.

Even in Canada with the use of the two newer dicamba products there have been problems, however, despite the demonstrations at the 2015 Outdoor Farm Show, where ground and wind speeds, water volumes, nozzle types and pressures, boom heights, and the need to avoid thermal inversions that create the potential for off-target movement were all covered. In 2017 and 2018, there were still sporadic reports of damage using the Xtend soybean system.

It’s a puzzling predicament, but one that might not be surprising, given the success the chemical industry has provided through the years. In the 1970s, the wonder product that came to market was atrazine, followed by the Group 2 product lines. By the mid-1990s, resistance began to show up in those products… until 1997, when the introduction of Roundup Ready soybeans — and the use of glyphosate — solved the Group 2 resistance crisis. Time and again, science and the chemical industry have united to solve emerging resistance challenges, arguably with superior and more convenient technology each time.

That’s one of the misconceptions to come with dicamba-tolerant (DT) technology: it’s not a “silver bullet.”

While it’s an excellent tool to be used on the farm, says Anita Speers, crop input specialist with Lakeside Feed & Grain Ltd., in Forest, Ont., the belief that dicamba will solve all of a grower’s glyphosate-resistant weed problems is a setup for failure. In reality, it’s more like another piece of their crop-protection puzzle, since it offers some residual activity on broadleaf weeds and adds a different mode-of-action into the tank.

“A second misconception is that the new formulations of dicamba won’t drift or volatilize like the old formulations,” says Speers. “Looking at how these new dicamba products have been formulated, there have been great strides in reducing the amount of volatility that takes place, but unfortunately, volatility is something that is out of a producer’s hands. There are many external factors that influence how dicamba will move and potentially cause damage to a sensitive crop.”

Even small amounts can damage a soybean crop, as demonstrated at the 2017 Outdoor Farm Show. With two growing seasons almost complete, a plot demo showed dicamba’s potential for crop damage and yield loss. During the display, Mike Cowbrough, weed specialist with the Ontario Ministry of Agri­cul­ture, Food and Rural Affairs (OMAFRA), discussed the level of damage caused by dicamba, following extensive rinse procedures. He said one research paper cited a 10 per cent yield loss in soybeans at 0.16 per cent of label rate of dicamba while others (from U.S. farm media sources), quoted research findings of 30 to 40 per cent yield loss. Visually, plants sprayed after four serial rinses showed cupping in the leaves.

Some answers

It may sound a little like a remedial class in how to use dicamba, but it’s worth repeating that there are several ways to avoid damaging crops. The first is to understand the technology’s timing, which can be summed up as “the earlier the better.”

“It’s linked to the maturity of the soybeans,” says Eric Richter, territory sales representative for Prince Edward Island and Nova Scotia, with Syngenta Canada. “Short- or even mid-season beans will have more significant impact on reducing the reproductive capability of the plant.”

Richter praises the industry for recommending that the Xtend system and a corresponding herbicide product be used during the early part of the growing season, in most cases as a pre-emerge.

Another recommendation is for more thorough planning of herbicide programs. Speers maintains that dicamba is an excellent technology but it also takes time and patience to use it in the most effective and economic manner. Produc­ers, she adds, must look at their individual farm needs, not at what the neigh­­bour’s farm needs.

The important point is, deciding to grow dicamba-tolerant soybeans doesn’t mean you automatically have to spray dicamba as part of your herbicide program.

“Take the time to do a self-check,” she says. “Do I have the time to properly clean out my sprayer? Do I have the resources to properly apply dicamba? And does the weed spectrum on my farm line up with the list of weeds on the dicamba label? If you answered ‘No’ to these questions, I’d recommend against using dicamba at all.”

Instead, she suggests looking at products that are better suited to managing the weed spectrum on your farm, a message offered repeatedly by many researchers including Dr. Peter Sikkema of the University of Guelph. Speers notes that producers may find that dicamba isn’t the right fit, especially if they’re dealing with glyphosate-resistant Canada fleabane (GRCF). A product like metribuzin, found in Sencor or Boundary, is more effective on GRFC.

Mix it up

One other strategy that’s been stated in the past yet bears repeating is the need for tank mixes. The days of one-pass, one-active ingredient weed management are gone. The ongoing problems with GRFC, common and giant ragweed, and the increasing potential for common waterhemp make that a necessity. Using the current technologies available to growers, the practice of tank mixing is the only course of action.

“Once growers have a handle on what chemical modes of action match their problematic weeds, it’s important to start looking at the modes of action used on their operation,” says Speers.

“Under­stand­ing the need to mix things up is more than just spraying product ‘A’ in 2018 and then spraying product ‘B’ in 2019. Producers need to look at the big picture of their spray program: what modes of action are in the tank for corn or wheat or dry beans?”

Richter agrees the times have changed, as much out of necessity as the introduction of new technologies and their accompanying products. There’s also the body of work by researchers like Dr. Clarence Swanton from the University of Guelph who have redefined the stages at which crops like corn and soybeans “detect” the presence of nearby weeds, which have a negative impact on crop development and yield. It’s against that background that practices have changed.

“(The need for multiple modes of action) has been a strategy or direction that companies, including Syngenta, have taken, and not just with herbicides but with fungicides and insecticides,” says Richter. “If you look at the majority of our products now, regardless of the crop that’s registered for, we’ve moved away from single A-I products to combined multiple modes of action, and this is a good example of this.”

Unfortunately, it’s unlikely that dicamba-tolerant systems will have the same longevity as the glyphosate-tolerant technologies before it. Speers believes the countdown may have already started regarding its durability.

“It’s a good technology, but it cannot be abused like the glyphosate-tolerant system was,” she adds. “If producers do not implement proper resistance management strategies, it’s only a matter of time before the first case of dicamba-tolerant weeds rear its ugly head in Ontario.”

Like the days of single-pass, single-active weed control, taking the approach of “But I’ve always done it this way,” are no longer effective. The agri-food industry is in a constant state of flux, changing and growing, and in order to add longevity to available technologies, producers must change their outlook on the use of certain products.

“On the whole resistance subject surrounding weeds or pests in general, growers young and old are now starting to realize resistance management has to be a best management practice, front and centre,” says Richter. “And that’s the way not only for this coming season, but also for the season after that and the one following that. It has to be a long-term outlook.”

This article was originally published in the February 2019 issue of the Soybean Guide.

About the author

CG Production Editor

Ralph Pearce

Ralph Pearce's recent articles



Stories from our other publications