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Herbicide tolerant weeds growing concern

“Once you see herbicide resistance in a field it’s been there a number of years. You just didn’t notice it.

“Once you see herbicide resistance in a field it’s been there a number of years. You just didn’t notice it.”
— BASF Technical Marketing Specialist
Bryce Geisel

Herbicide resistance in a growing number of weeds is becoming a problem producers must be aware of.

The first herbicide tolerant weed was discovered in 1975, BASF Technical Marketing Specialist Bryce Geisel told those attending a BASF Knowledge Harvest event held in Yorkton last Thursday.

Since then the number of herbicide tolerant weeds has shown “a pretty strong trajectory going up,” he said, adding “I’m pretty sure the line will keep going up as years go on.”

At present the United States is showing the greatest problem with 132 different weeds being identified as being herbicide tolerant to at least one product, said Geisel.

Australia shows the second highest concentration of herbicide tolerant weeds, with Canada third in the world with some 62 identified.

The three Prairie provinces all have herbicide tolerant weeds, said Geisel. In terms of the local Yorkton area he referred to the 2014/15 Agriculture Canada Weed Survey which showed the most prevalent herbicide tolerant weed is volunteer canola from varieties genetically bred with a tolerance.

Second on the list are wild oats, followed by green foxtail and wild buckwheat, each showing tolerances to certain herbicides in some populations.

Geisel said not all herbicide tolerances are the same.

The simplest resistance has a population of weeds evolving to resist a single active ingredient used in herbicides, he said.

The second level has plants developing cross resistance, or to two active ingredients, which reduces the options in terms of how to control the weeds.

And then there are weed populations with multiple resistance, an issue being seen “primarily in wild oats” in Western Canada.

Multiple resistance “really starts limiting” what farmers can use in terms of herbicides for effective control, said Geisel, adding they are seeing that happening more and more in the U.S..

The problems of herbicide tolerance “start when using the same herbicide over, and over, and over again,” said Geisel.

While, Geisel noted “herbicides do not induce herbicide resistance” when it begins to occur repeated use of the herbicide allows resistance weeds to mature, and set seed, which over time increases resistant populations.

Of course the problem is identifying resistance before it becomes a major issue.

“Once you see herbicide resistance in a field it’s been there a number of years. You just didn’t notice it,” said Geisel.

Geisel said the best prevention is to vary things so resistance populations have a much hard time becoming established. That means rotating crops which facilitate a more varied herbicide package being used.

In extreme cases resistance weeds could facilitate more drastic changes in farm techniques, including more tillage, or the use of cover crops which add costs and time to managing a field.

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