Weed management | Herbicides on bare ground increase risk of glyphosate resistance
There is one thing growers can do immediately to stem the tide of herbicide resistant weeds, says a weed expert.
“I would like to see chem fallow eliminated because it is a breeding ground for glyphosate resistance,” said Hugh Beckie, Agriculture Canada’s herbicide resistance expert.
Bad things happen when growers apply herbicide to bare ground, he said during a presentation at the 2014 Canola Discovery Forum and in a later interview following his speech.
“Your risk of glyphosate resistance in whatever weed increases dramatically, mainly because there’s no crop competition,” said Beckie.
Read Also
Land crash warning rejected
A technical analyst believes that Saskatchewan land values could be due for a correction, but land owners and FCC say supply/demand fundamentals drive land prices – not mathematical models
Growers who chem fallow use high rates of herbicide multiple times throughout the year, which is another sure-fire way to promote resistance.
The amount of land chem fallowed every year is declining, but significant acres are still idle every year in places like southern Alberta and west-central Saskatchewan.
Part of the problem is that farms have become so large that growers can’t cover all the ground that needs to be seeded in spring. As a result, chem fallow remains a regular farming practice for some growers. For others, it is an emergency measure for unexpected events such as spring flooding.
Beckie would much prefer farmers to seed idle land to annual or perennial cover crops that can be planted well into June, long after the spring seeding season.
“There is a lot of research going on in terms of cover crops that can self-destruct before they compete for moisture or nutrients in the next crop,” he said.
Annual or perennial crops dramatically reduce weed seed banks.
“If you can drive down the weed seed bank without herbicides, you’re way ahead of the game,” said Beckie.
A lot of growers feel that crop rotation is the best line of defense against resistant weeds.
Surveys reveal farmers are rotating four or more crops a lot more than they did in the 1990s, but growers shouldn’t be too quick to pat themselves on the back.
“You have to ask yourself, is that real crop diversity?” he said.
Farmers are just switching from one spring-seeded, cool season crop to another. They’re all planted at the same time, sprayed at the same time and harvested at the same time.
“I would argue that is not diversity,” said Beckie.
“We still have very few fall-seeded and perennial crops.”
A long-term study on cropping systems at Agriculture Canada’s Scott Research Farm in Saskatchewan has demonstrated that a diversified rotation that incorporates a perennial crop such as alfalfa significantly reduced the level of wild oat herbicide resistance.
In fact, there was barely any resistance, even in a system where six applications of Group 1 herbicides were applied over an 18-year period.
By comparison, 42 percent of the wild oat population was resistant in a diversified grain rotation that had 10 applications of Group 1 herbicide over an 18-year period.
“This just demonstrates the impact of real crop diversity on resistance management,” said Beckie.
He recognizes that growers are reluctant to incorporate three years of alfalfa in a six-year rotation, but there needs to be some new approach to weed management other than continued reliance on herbicides.
“Worldwide, we’re really at a tipping point in terms of resistant weed management because we have an explosion of weeds that are resistant to multiple modes of action,” said Beckie.
More than 70 weeds are resistant to two or more modes of action, including wild oats in Western Canada, which are resistant to Group 1 and Group 2 herbicides.
As well, a new mode of action hasn’t been made available to farmers since 1982.
Beckie said short-term help is coming in the form of new genetically modified crops containing stacked traits. For instance, Dow AgroScience recently received U.S. Department of Agriculture approval for its Enlist corn and soybeans, which are tolerant to glyphosate and a new form of 2,4-D.
However, he believes the stacked trait crops will eventually exacerbate the problem with multiple resistance.
“It’s not a long-term solution,” said Beckie.
“The long-term solution is we have to start reducing our herbicide use.”
He believes governments have a role to play in providing financial incentives for growers to adopt best management practices.
One best management practice for soil conservation is having a negative effect on weed resistance.
The move to no-till systems has facilitated weed resistance because weed seeds are concentrated near the soil surface rather than buried deep in the profile where they may not germinate.
The turnover rate from seed to weed is much faster in no-till systems, which leads to increased resistance.
As well, Beckie said the crops grown on those no-till fields are also contributing to the problem. Contrary to what seed technology companies preach, today’s GM canola crops use more herbicides than the non-GM crops grown in the 1990s, he added.
