Pull weed, you know it's dead

Back in the days when a penny was still worth five Mojos at the local store, Grandpa paid us a cent a plant one hot July afternoon to hand-pull the non-conforming plants out of his seed oat crop.

If some agronomists are correct, farm kids of the future might also benefit from a similar entrepreneurial experience.

Hand-weeding -- as well as every other means of offing herbicide-resistant weeds before they go to seed -- is now promoted as a measure farmers should consider if they want to avoid a creeping invasion of weeds that don't respond to herbicides.

They call them "escapes," a few weeds left standing after a herbicide treatment that should have killed them. Farmers get fooled, thinking the sprayer missed them. So they go to seed. One weedy plant that goes to seed can distribute hundreds of thousands of seeds carrying the same resistant gene.

It was only a few short years ago that stories started to surface about U.S. cotton farmers whose farm trucks, once loaded with herbicide containers, are now filled with hoes. That was safely far away.

But when provincial agronomists visited fields just across the border in North Dakota last year, they found fields infested with weeds resistant to at least one, and in some cases, multiple herbicides.

Herbicide tolerance is a double-edged sword. It's a good thing to have crops that can survive a herbicide application while all the weeds around them die. But a weed is a plant in the wrong place at the wrong time, not necessarily a bad plant. That means seeds from last year's crop can germinate and turn into this year's weed.

Nature doesn't distinguish between the two and has proven extraordinarily capable of breaking down the artificial barriers scientists and farmers keep trying to erect.

While crops modified to resist certain insects have been shown to use fewer pesticides, the opposite is true for herbicide-tolerant crops, which are now starting to need "stacked traits," or more than one type of herbicide in the mix, to get the job done.

Some weed scientists are openly questioning the industry's single-minded focus on herbicides, particularly the introduction of stacked traits, to address the growing problem of herbicide-resistant weeds.

"Why are so many weed scientists and extension personnel recommending more herbicides to mitigate herbicide-resistance problems?" asks an editorial by six leading Canadian weed researchers, Neil Harker, John O'Donovan, Robert Blackshaw, Hugh Beckie, C. Mallory Smith and Bruce Maxwell, published last year in the journal Weed Science.

These researchers argue promoting "herbicide diversity" and stacked-trait technology as the solution to herbicide-resistant weeds is short-sighted at best. "Multiple resistance to herbicides with different sites of actions has occurred in the past and will increasingly occur in the future," they say.

They call for greater diversity in the crop rotation, more focus on integrated pest management and fewer in-crop applications of glyphosate, the non-selective herbicide that is the active ingredient in Roundup Ready crops. Once thought to be infallible, there is a growing list of weeds worldwide that have developed resistance to it.

"Are we a discipline so committed to maintaining the profits for the agrochemical industry that we cannot offer up realistic long-term solutions to this pressing problem?" the weed researchers ask.

In a 2011 essay, Robert Zimdahl, a retired weed scientist from Colorado State University, eloquently describes the tunnel vision that has displaced biological logic.

"Most biologists accede to the view that their research is contributing to an expanding view of nature that will never be complete. However, in some sectors of biology, and I think especially in weed control, scientists may not operate from this broader biological perspective. We know weed control is evolving, but its evolution has been constrained because 20 years ago the science focused almost exclusively on a single solution to the problem. The desirable goal of weed control was too frequently hitched to the technological achievement of herbicides."

Farmers often complain they can't control the weather, nor can they control the markets, but on this one, they are in the driver's seat because they choose what to grow on their farms. However, they continue to be easily swayed by simple solutions to this complex problem.

Next week: One U.S. researcher is taking the concept of crop rotation to a whole new level.

Laura Rance is editor of the Manitoba Co-operator. She can be reached at 204-792-4382 or by email:

laura@fbcpublishing.com

Republished from the Winnipeg Free Press print edition February 9, 2013 B9