Researchers find that residues in dry bean crops can increase dramatically when crop maturity drops below 75 percent
A University of Guelph dry bean expert says glyphosate can be used as a pre-harvest aid, but it really should be tank mixed with a true desiccant.
Chris Gillard, who led a study that cost about $1.2 million to evaluate the performance of glyphosate and other products for desiccating dry beans, said dry bean exports from Canada are regularly tested for glyphosate residues.
Gillard’s three year study, which was mostly funded by Agriculture Canada and bean grower and bean dealer associations, found that glyphosate residues from dry bean plots in Alberta, Manitoba and Ontario rarely exceeded maximum residue limits (MRLs) if applied at the right time. However, timing a glyphosate application before harvest can be challenging in the real world.
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“Glyphosate on the label says 100 percent of the pods must be mature. We were a bit early on the glyphosate side and still didn’t find any residues that were in excess of the MRLs allowed for glyphosate to our export markets,” Gillard said.
“(But) our studies were small plot research, so the crop is relatively even in that small area. What growers are faced with is uneven maturity…. (Maybe) he’s got some crop that’s near 100 percent maturity and he’s got some crop that could be at 50 percent pod maturity. So when do you pull the trigger?”
Gillard and his colleagues found that glyphosate residues in dry beans can increase dramatically when crop maturity drops below 75 percent.
“If glyphosate is applied prior to beans reaching 75 percent maturity, then glyphosate residues may exceed acceptable limits of two parts per million,” the authors wrote in a paper published earlier this year in the Canadian Journal of Plant Science.
Gillard said glyphosate trans-locates in the plant when the tissue is still alive and can accumulate in the seed and the pod.
True desiccants don’t move through the plant.
“Their translocation … is almost zero,” he said.
“They get sprayed on the leaves and stems. They penetrate in, they don’t move…. They just penetrate into the tissue, then blow it up.”
The Hensall District Co-operative in Ontario, which exports dry beans, is concerned about dry bean growers who exclusively use glyphosate as a pre-harvest aid.
The co-operative has language in certain dry bean production contracts that require growers to apply a desiccant other than glyphosate.
“The glyphosate MRLs are tighter in some countries than others,” said Brad Chandler, commercial business manager of the co-op’s food products division.
”If we know the crop … is going into a designated area where we know the glyphosate MRL is tight or could be a challenge, we will try to steer the growers away from using glyphosate or any other product that has a low MRL,” he said.
Chandler said Japan and the European Union are the markets of biggest concern when it comes to glyphosate residues on dry beans.
“If we’re going to participate in exporting of these grains, or dry beans or whatever product, then definitely we have to be aware of these MRLs and then manage them with the growers.”
Pulse Canada and the provincial pulse associations in Western Canada remind growers every year to apply desiccants such as Heat and Reglone and harvest aids such as glyphosate at the proper time and rates.
Francois Labelle, Manitoba Pulse & Soybean Growers executive director, said production contracts for dry beans often require growers to avoid certain crop products, but it’s not just glyphosate. Buyers and exporters are worried about MRLs for a variety of products.
“It’s not only on edible beans, it’s on all crops that people need to pay attention to…. It could be on wheat, or just about anything. If you have the wrong product put on, it could have an effect.”
In a separate paper, which was also published in the Canadian Journal of Plant Science, Gillard and his colleagues found that glyphosate is more effective when used in combination with a real desiccant.
“This study concludes that diquat, glufosinate ammonium, flumioxazin and saflufenacil alone or in combination with glyphosate … when used as a harvest aid can provide consistent desiccation of dry bean,” the authors said.
robert.arnason@producer.com
- More than 10 varieties of field beans are grown in Canada.
- The main types are navy, pinto, black, red Mexican and red kidney.
- Varieties in limited production include cranberry (romano), pink, great northern and Dutch brown.
- Manitoba is the top bean producer in Canada in terms of seeded acreage, with 140,000 acres in 2014, compared to Ontario at 130,000 and Alberta at 45,000.
- In 2013-14, Canada exported 304,000 tonnes of dry beans, and is expected to export 305,000 tonnes in 2014-15.
- Total production for 2013-14 equaled about 232,000 tonnes.
