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Apr 11

Study sheds new light on fighting wild oats

Posted on Apr 11 By: Tyler Difley

Agriculture and Agri-Food Canada Research Scientist Neil Harris said most wild oats will be resistant to at least one herbicide in the next few years because the same sprays are used over and over again. Credit: Tyler Difley
A recent study concluded cultural practices present an attractive alternative to herbicide alone when controlling wild oats in barley. According to the report, which was published in the journal Weed Science, optimal cultural practices combined with herbicides are a farmer’s best bet to reduce the wild oat seed in the soil seed bank and increase barley yields.

Conducted by Agriculture and Agri- Food Canada (AAFC) scientists John O’Donovan, Neil Harker, Kelly Turkington and George Clayton, the study identified wild oat as the number one weed problem in Western Canada. The study said the weed causes millions of dollars in yield losses, as well as $500 million in herbicide costs on an annual basis.

Harker said this was especially problematic as wild oat was rapidly developing herbicide resistance which could make it far more difficult to control with traditional chemical treatments.

“There will come a point in a few years from now where most of our wild oats will be resistant to at least one herbicide and possibly cross resistant to some others, just because we continue to use the same herbicides over and over,” said Harker. He added that currently, about 50 per cent of Alberta wild oat populations are resistant to group one herbicides.

In the study, the scientists addressed the ever-expanding number of herbicide-resistant weeds and the need to prevent weed seed accumulation in the soil seed bank using cultural approaches as part of a sustainable weed management strategy.

The study itself examined three cultural practices for controlling wild oats: seeding rate, crop rotation and variety selection. It compared rotations of barley, canola and peas to ones of continuous barley, normal seeding rates to twice the normal seeding rates, and tall barley varieties to semi-dwarf varieties. It also experimented with different herbicide applications, using variations of 25, 50 and 100 per cent of the recommended rates for the various tests.

“There are cultural practices that when combined—such as combining a good rotation with seeding a higher than normal seeding rate in competitive cultivars—can do as well as a high herbicide rate,” said Harker. “What that allows you to do is to reduce selection pressure for weed resistance.”

According to the study’s findings, implementing a diverse rotation and seeding barley at a relatively high rate proved most successful. Varietal selection did not have as large an impact as seeding rate and crop rotation.
The first phase of the study ran from 2001 to 2005 at four locations across Western Canada. Phase two continued from 2005 to 2009 at two of the original locations: Beaverlodge and Fort Vermillion.

Regardless of herbicide rates, the study found that the highest barley yields occurred with optimal cultural practices. This indicates that these cultural practices—like rotation and seeding rates—could mitigate yield losses when herbicide proved less effective.

In fact, the scientists noted that at the Beaverlodge location, wild oat numbers were reduced 40-fold by a combination of optimal cultural practices and the recommended rate of herbicide.

Interestingly, the scientists also found that hulless barley varieties tended to be less competitive with wild oat than standard hulled varieties.

According to Turkington, studies like this one are beneficial in large part because of their multi-disciplinary, multi-locational nature.
“We have collaboration amongst colleagues in different areas of expertise, as well as over a wide range of environmental and soil conditions,” said Turkington. “Thus, we are taking a holistic, integrated approach to develop strategies that promote crop productivity and quality, limit pest impacts and reduce input costs.”

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