Trouble looms with shorter canola rotation, warns expert

An Agriculture Canada researcher issued a cautionary message last week to an audience of canola industry members.

Neil Harker said the two-year canola rotation that dominates the Prairies comes with inherent risks that threaten future production of the crop: increased levels of disease and pests and the breakdown of variety resistance.

“I think we’re at a point where we shouldn’t just say more and more is better,” Harker said.

“We’ve had record production. Perhaps we should look for some opportunity to go elsewhere. The canola industry needs to act decisively soon.”

Canola acres in Western Canada have grown dramatically, from 12 million acres in 2000 to 20 million in recent years, putting as many as one-third of prairie acres into canola production.

“How do we promote biodiversity in a cropping system that has essentially two components?” Canola Council of Canada agronomist Greg Sekulic told the Saskatoon meeting.

“If you ever want to see a sea of eyes go blank, stand in front of a group of farmers and tell them that the only way to do that is to have a four year rotation.”

Growers have found that a two-year crop rotation of canola and wheat is the most profitable, although re-search has found better canola performance in a three-year rotation that includes peas.

“We can’t fault producers for taking advantage of a good climate to recover costs they lost in a bad year,” Harker said in an interview.

“You can take advantage of that for a few years, but eventually if you keep that same tactic, you’ll have problems, and it won’t be economic anymore.”

The shorter rotation increases the chances for the buildup and spread of diseases, such as blackleg and clubroot, and herbicide resistant weeds. Western Canada has already seen the spread of glyphosate resistant kochia.

Sekulic said the industry has taken steps to reduce chemical use, primarily insecticides, to maintain populations of beneficial insects and honeybees. Economic thresholds are being adhered to “quite well,” he added.

He also said researchers have found that altering herbicide applications so that they leave some weed populations can reduce root maggot damage with minimal economic loss.

“(That’s) one reason to potentially not apply that second application of herbicide and pushing off some potential resistance while at the same time getting a whole lot less root maggot damage,” said Sekulic.

Harker said Roundup Ready corn, soybeans and cotton have been continually cropped in the southern United States with consequences.

A survey earlier this year found that almost half of U.S. farmers have reported glyphosate resistant weeds.

In Arkansas, cotton acres have fallen by almost two-thirds since 2005, and other states have seen similar drops.

It’s partly due to the economics of the crop but also because of multiple weed resistance that has decreased the utility of glyphosate.

“I think the more we repeat something over and over and over again, the more that Mother Nature finds a way around it, whether we’re putting pressure on a specific group of weeds or insects or diseases,” said Harker.

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  1. Joe Sierens on

    Can someone explain to me why leaving weeds in our fields will help reduce root maggot perhaps I miss understood please help clarify this.

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