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Wheat & Chaff – for Apr. 5, 2010

Wheat &


Each issue of Grainews has a theme. This issue is all about weeds and weed management, which in most cases means we talk about herbicides. Herbicides are the most widely used pesticide in Canada, accounting for $1.5 billion of commerce each year. It’s no wonder, really, seeing as these moisture-and fertilizer-using pests can easily steal five per cent of a crop’s yield potential just by being up and growing before the crop. The good news is that western Canadian farmers are doing a good job of using herbicides responsibly and sustainably. The bad news is biology conspires against us at every turn and despite our best efforts, can hand us herbicide resistance.

I had a great conversation about integrated weed management (IWM) on the Prairies with Bob Blackshaw, a weed scientist with Agriculture and Agri-Food Canada in Lethbridge. IWM is a strategy to control weeds combining the use of herbicides and cultural practices for greater overall control of weed populations.

When asked what farmers are doing right, he easily rattled off five or six management practices that have gained in popularity over the last few decades. Wait… decades? Well, yes. Changing management practices is an evolution, a process, not an on/off switch.

I’ve put together Bob’s list of what you’re doing right, and the spin-off benefits of each practice on page 6. I’ve also added the two things that he’d like to see farmers adopt next. One — cover crops — is a little “out there” for most conventional growers, but zero till was a little out there when the idea was first introduced over 20 years ago.

Zero till, Blackshaw says, is possibly the number-one weed-destroying management practice that farmers have mastered. The beauty is that zero till makes sense for a list of other reasons, such as moisture retention and decreased soil and water erosion. Weed suppression and elimination is an unintended, but very welcome, side benefit.


The beauty of integrated weed management is that each individual practice, such as higher seeding rates, zero till or spring versus fall fertilization, benefits the crop and is detrimental to weeds. But when combined, the benefits multiply. In short, by combining herbicide use with three or more other management practices, each individual weed control strategy works better. Call it one plus one equals three, Blackshaw says. Every new layer of management added to the overall weed-control strategy stretches those benefits further.

For example, zero tillage results in fewer weed seeds germinating. Weed seeds left on the soil surface are more likely to picked up by birds and rodents or exposed to the elements to die before becoming viable. But that’s not the only way zero till fights weeds. Higher snow-trapping and less drying out of the soil means more available soil moisture. Over the last three decades, this additional moisture has made it possible to get away from just growing cereals and adding pulses and oilseeds into the rotation.

Adding crop diversity doesn’t just help manage price risk, it also breaks weed, disease and insect life cycles by depriving certain pests of host crops. What’s more, rotating from one crop to another allows the use of different herbicides, which is instrumental in preventing any one weed from getting away on you.

“There are many areas of the Prairies where we wouldn’t dream of ever growing canola or pulses because we thought it was just too hot and too dry,” Blackshaw says. But with zero till and variety development, it’s been not only possible, but downright successful.

Blackshaw says that when the move to zero till started in earnest, there was some vocal backlash regarding the perception that zero till would require more herbicide applications. In truth, nearly 25 million acres are no longer left fallow in Western Canada, but our herbicide usage has remained essentially constant. It means that we’re growing 25 million more acres of crop with the same amount of chemical — that’s a good news story and one we should be talking about.

Zero till does create some problems, ones that savvy western Canadian growers are already finding ways to work around. Biology is a crafty thing, and different weed types have taken hold in the system. The shift to more winter annual and perennial weeds means that post-harvest weed control becomes more important, as does early spring burn-off.


A wise rancher once said to me (and I don’t know where he got it from, so my apologies if this is your quote), “Focus on what you want, not what you don’t want.” In weed-management terms, if the focus is on creating a healthy, vigorous, optimal plant stand, the weed management follows. “What’s good for the crop is bad for weeds,” Blackshaw says.

What’s missing on many farms, he says, is an overall plan and strategy to put all these weed management practices together. Many farmers are doing many of the right things but by taking a big-picture view of all cropping practices, they might find a hole or one particular piece of the management puzzle that’s missing.

“By combining two, four or five of these weed-control practices, you really start to reap the benefits,” he says.


I’ve made a point to talk about herbicide resistance management extensively in this issue of Grainews. Why? Because here in Canada, we’re in a relatively good position — glyphosate-resistant weeds are not yet an issue, and we have several herbicide groups at our disposal. The problem is, while I don’t want to be alarmist, we can’t be complacent. There are already several herbicide-resistant weeds on the landscape and at least one confirmed glyphosate-resistant weed in Ontario. As Blackshaw says, the idea of glyphosate-resistant kochia gives him nightmares.

What can we do to deter resistance? Many of the management tools are things you do already because they’re good for the crop, such as one-in-three-or one-in-four-year crop rotations. How closely do you keep track of the herbicide groups you use for post-harvest, pre-seeding and in-crop applications? Rotating between groups each time is not just a good idea, it’s necessary to extend the life of the chemistries we have on hand.

In this issue, I’ve tried to put together a few stories that can help you develop a herbicide-resistance strategy for your farm. Gerald Pilger has put together an eye-opening and informative question and answer on what weeds to worry about and how to slow resistance in Western Canada (see page 5). Jay Peterson has done a great job of spelling out what you need to do if you suspect weed resistance (see page 12). Angela Lovell tackles the issue of glyphosate resistance in herbicide-tolerant canola, which is thankfully a good news story (see page 14).

The bottom line is, herbicide resistance occurs when herbicides are used. It’s up to farmers to take the necessary measures to manage it.


I hope you enjoy this issue of Grainews. Please stay safe out there during seeding and I promise to hope for rain when you need it and sunny skies and warm weather when you need that, too. Do me a favour and when you think of some great story idea on the tractor, give me a call (306-731-3637) or send me an email ( It’s [email protected]

great to hear from you. Cheers, Lyndsey

Lyndsey Smith Editor, Grainews

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