Applying glyphosate before harvest isn’t a significant concern when it comes to herbicide resistance, says an Agriculture Canada weed expert.
“It does add some selection pressure, but a lot of the selection has (already) taken place. You’re mostly just drying down the crop,” said Neil Harker, Agriculture Canada weed scientist in Lacombe, Alta.
“What’s left when you’re desiccating are weeds left over from the other treatments, so (with) much less population, selection pressure wouldn’t be as high…. So I’m not as concerned about it.”
Hugh Becky, an Agriculture Canada weed scientist and herbicide resistance expert, agreed using glyphosate as a desiccant shouldn’t exacerbate resistance. Still, producers should monitor how often they use the herbicide during the growing season.
Harry Brook, an Alberta Agriculture crop specialist in Stettler, said spraying glyphosate before harvest has become standard practice for many cereal growers.
He said straight combining is growing in popularity because farmers don’t have the time or manpower for both swathing and combining at harvest time. With swathing on the wane, desiccation has become a harvest necessity.
“People have moved to … straight combining, and you can’t do that if you’ve got green spots in the field. You must use something to dry down that crop and get even maturation,” Brook said.
“It’s part of a system of farming…. With a sprayer … you can cover a whole lot of acres in a short time.”
Harker said growers choose gly-phosate as a desiccant because it’s cheap and they get an additional bang for their buck. The herbicide kills perennial weeds.
“It’s not an ideal desiccant. If weather conditions don’t co-operate, it can take more than two weeks to dry things down…. The standard desiccants would do it in two or three days, no matter what the conditions are,” Harker said.
“A lot of guys (say), ‘oh well, it’s not a great desiccant… (but) it will get some of my weeds, especially the perennials.’ ”
Brook said cereal growers use glyphosate as a desiccant because there aren’t many options to achieve uniform maturity within a field.
However, farmers who regularly use glyphosate as a desiccant may not be using the product wisely, Brook said.
“It’s not a desiccant at all. It’s a herbicide that terminates plant growth,” he said.
“Glyphosate is a tool. It’s like a toolbox. You don’t use the hammer to screw in a screw…. Glyphosate is a good multi-tool but it shouldn’t be overused…. Sometimes swathing can be a better alternative.”