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Canola maturity matters in desiccation timing

The Canola Council of Canada’s Spray to Swath calculator shows 
just how long to wait after spraying a desiccant or other pre-harvest chemical

swathing canola

In desiccation — as in life — success is usually defined by maturity.

The right time to apply a pre-harvest desiccant is when the crop is physiologically mature, says crop specialist Harry Brook.
The right time to apply a pre-harvest desiccant is when the crop is physiologically mature, says crop specialist Harry Brook. photo: Jennifer Blair

“Whatever product you’re using, make sure you’re using it when the majority of the plants in the field is physiologically mature,” said Harry Brook, crop specialist with Alberta Agriculture and Forestry.

“You get into problems when they’re immature. It doesn’t preserve your yield or your value when you’re using it.”

Desiccants can help dry down the crop for an earlier harvest, said Brook, who spoke at the Making the Grade workshop in late July. Right now, four products — Syngenta’s Reglone, BASF’s Heat, Nufarm’s Aim, and glyphosate — are used as desiccants in Canada.

But desiccants don’t help immature seeds to mature, said Brook, so it’s important to apply any desiccant when the plant is already mature.

“Physiological maturity occurs at basically less than 30 per cent moisture. That applies for all cereals, peas, and canola,” he said.

In canola, the right stage is when 60 to 75 per cent of the seeds have changed colour. Cereals are mature when “the part just below the head of the stem is yellow and dry,” he said.

At that point, producers should be doing the ‘fingernail test.’

“Try and force a crease down it,” said Brook. “If you can see a dent in the kernel and it stays in the kernel after taking your fingernail off, then it’s at 30 per cent (moisture) or less.”

Pre-harvest intervals — “meaning the time from when you apply a product to the time you cut it” — are equally important, said Keith Gabert, an agronomist with the Canola Council of Canada.

And the best place to get information on pre-harvest intervals in canola is the Canola Council’s Spray to Swath calculator, he said.

“If you’ve already sprayed and you know what you’ve sprayed, you can put that product in there and it will tell you how many days you need to wait,” said Gabert. The calculator (available at also allows producers to pick when they want to swath, and will choose a product based on that timeline.

Following the right pre-harvest intervals and making sure the crop is mature when it’s sprayed will help keep any residues within acceptable levels for export, said Brook.

“If you do it when it’s not mature, that’s when you get the chemical getting into the grain itself, which affects the quality,” said Brook.

“Ultimately, that’s when we start getting feedback from the customers buying the stuff saying, ‘What’s with these maximum residue limits being too high?’”

That’s why following the product label is so important, added Gabert.

“These pre-harvest intervals are typically designed because the companies have done the tests to show that your product — the food that we sell somebody else — is now below the maximum residue limits if you wait the right number of days,” said Gabert.

“It’s really critical that you understand that and read and follow label directions.”

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