For Effective and Sustainable Weed Control, Use the Big Sledgehammer Less Often

Owen RobertsWhy do we speed when we know it’s wrong? Why do we text while driving? Why smoke, when we know it’s bad? Why continue overusing traditional chemistry herbicide applications when we know they’re causing problems?

That’s what Canadian weed scientists want to know.

They’re getting frustrated with what seems to be farmers’ general unwillingness to adopt integrated weed management (IWM) strategies, despite being told repeatedly they’re hamstringing their own businesses long-term and doing agriculture’s image a disservice by ignoring experts’ advice.

“We should be seeing a drop in pesticide use,” says Dr. Hugh Beckie, a weed researcher at Agriculture and Agri-Food Canada and outgoing president of the Canadian Weed Science Society, “but we’re not. Reduced pesticide application is our metric, and it’s vital for managing resistant weeds. But it’s not happening.”

Beckie, speaking from the Canadian Weed Science Society annual meeting in Montreal earlier this week, says farmers in conventional cropping systems are indeed incorporating some aspects of IWM, such as crop rotation and increased seeding rates.

But overall, he says, there’s resistance to change, likely for a couple of reasons.

First, farmers still don’t accept what’s now become an age-old idea in science – that is, some weed presence in your fields will not significantly affect yields. Research-based critical thresholds exist – and none of them say all weeds must be removed.  Google “weed control threshold” and your province’s agriculture ministry and you should be able to find them.

Beckie says famers’ low tolerance for weeds is mainly due to the stigma attached to seeing any weeds in a field. Traditionally, in agriculture, “dirty” fields have been associated with laziness or ineptitude on the farmers’ behalf, as if they were either unwilling or unable to keep their fields clean. It’s a very inter-generational attitude, a part of farming culture.

But unfortunately, that zeal can also lead to excessive pesticide use, including prophylactic “just-in-case” applications.

To deal with the matter, Beckie says it’s time to get out the big guns.

Earlier this fall, at an international herbicide resistance summit in Washington, D.C., participants agreed they needed to enlist the services of sociologists and economists to convince farmers to change their ways and adopt more integrated weed and pest management.

They said more emphasis needs to be placed on reasons for integrated weed management beyond science, such as efforts to reduce the social stigma of having fields with a few weeds, or more accessible strategies that get across the economics of resistance.

“We can warn growers about the problem of resistance, but we need more hard numbers to clearly demonstrate that it’s economical, even in the short term, to implement integrated weed management,” says Beckie.

He thinks a regional approach may be the way forward, coming up with some good numbers that show how much specific resistance problems cost producers in Ontario, on the prairies, etc.

But even if that’s successful, it won’t solve a much bigger problem – that is, the lack of new chemistries to control conventional weeds.  At the same time resistance is increasing –particularly weeds’ resistant to multiple mode-of-action herbicides– Beckie says industry has not significantly invested in new modes of action for 30 years. And there’s nothing new in the pipeline for at least another 10 years.

So if farmers think simply turning to a new chemistry is going to be their main approach to integrated weed management, they’re wrong.  They won’t find much to turn to.  And resistance is destined to grow.

“We’re at a tipping point for controlling weeds with existing tools that are starting to fail,” says Beckie.

So what can be done?

Mainly, says Beckie, producers need to rely less on the big sledgehammer approach. “Think in terms of ‘little hammers’ that can get the job done in a variety of ways, rather than one ‘sledgehammer’ pesticide or herbicide,” he says.

He admits it’s not an easy sell because producers will sense the many-hammers approach to be more time consuming and perhaps more costly. And they likely have a point.

But is there anything more costly than multiple types of resistance? We’re going to find out.

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Owen Roberts

Owen Roberts directs research communications and teaches at the University of Guelph, and is president of the International Federation of Agricultural Journalists. You can find him on Twitter as

@theurbancowboy

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