focus on weed management
Is IWM DOA?
Everyone agrees integrated weed management is sound science and a very timely response to growing resistance issues — so how come almost nobody does it?
T
ype the phrase “integrated weed management” into your web browser and nearly two million results come up. Scan them briefly and you’ll find many are publications proclaiming the essentialness of this weed control practice. Information on IWM? Lots of it. Actual application on the farm? Not so much. Extolled for years as a way of controlling weeds while reducing input costs, IWM seems to be one of those agronomic practices that never quite made a successful leap from the pages of scholarly journals to the fields of Western Canada. “I think it’s perceived as kind of an intellectual university-type of concept as opposed to something a real farmer would do,” says Steve Shirtliffe, a plant science professor at the University of Saskatchewan in Saskatoon. That’s not to say IWM isn’t done at all. Neil Harker, an Agriculture and Agri-Food Canada plant scientist at Lacombe, Alberta, points out IWM simply means managing weeds with more than one method of control. There are four such methods: chemical, biological, cultural and physical. Virtually all farmers except organic producers use herbicides. So they’re already partway toward practising IWM without even knowing it. Unfortunately, that’s where they stop, says Harker. “One of the issues is that growers are used to quick action with herbicides. With other methods, you have to be much more patient,” he says. “Technically, IWM is adopted by quite a few people.
You don’t always need to spray Farmers consider themselves lucky if they don’t have to spray for weeds. But according to Gary Martens, not spraying is a matter of creating your own luck. Most farmers expect to use herbicides when they plant crops in spring. But Martens, a University of Manitoba plant science instructor, says the idea is to plant a crop in the hope of not having to spray. How do you do that? By using cultural practices. One such practice is crop rotation, says Martens, who practises integrated weed management on a micro-farm near Kleefeld in southeastern Manitoba. Winter cereals break dormancy early in spring and get ahead of weeds, limiting their effect. Thus, inserting winter wheat or fall rye into the rotation every few years can help suppress weeds. Breaking up a wheat-canola rotation with a three-year alfalfa stand can achieve the same effect. Another recommended practice is to plant annual crops early. This gives them a jump on later-emerging weeds such as green foxtail and red root pigweed. Higher seeding rates and narrow row spacing result in a dense plant canopy which provides greater competition against weeds. Yes, upping seeding rates and planting rows closer together increases seed costs. But increased yields can compensate for the higher expense. Martens also recommends growers use competitive crop varieties. For example, organic farmers like McKenzie hard red spring wheat, a lesser-known variety which seems to compete better against weeds. Some varieties of barley also appear to do the same. Besides general IWM, Martens also encourages farmers to use precision agriculture tools such as GPS, GIS mapping software and variable-rate controllers to make weed maps. Then, using these “agronomic eyes,” spray only the areas that have weeds. Martens says all the technology needed for this exists, although he’s not sure how many producers are actually doing it.
8 CROPS GUIDE
|
FEBRUARY 2013
By Ron Friesen But from a practical point of view, in my mind, there’s way too much reliance on herbicides and not enough reliance on the other methods.” Gary Martens thinks he knows why. A plant science instructor at the University of Manitoba, Martens was once criticized at a farm meeting for speaking about integrated weed management. Producers told him IWM may be all very well but it’s not economical at a time when some growers are taking advantage of high commodity prices to pay off debts still outstanding from the farm financial crisis of the 1990s. “Many farmers can’t afford to think long term. They think one year at a time,” Martens says. Put simply, IWM combines different agronomic practices in order to reduce reliance on any single weed control method. As one MAFRI publication puts it: “Controlling weeds with one or two techniques gives the weeds a chance to adapt to those practices. For example, the use of herbicides with the same mode of action (belonging to the same herbicide group) year after year has resulted in weeds that are resistant to those herbicides. The continuous production of certain types of crops also gives weeds a chance to adapt… Integrated weed management uses a variety of control practices to keep weeds ‘off balance.’ Weeds are less able to adapt to a constantly changing system that uses many different control practices, unlike a program that relies on one or two weed control tools.” There you have it in a nutshell. Overreliance on herbicides eventually reduces their effectiveness. Using a range of tools reduces dependence on chemicals to control weeds. That’s the essence of IWM. According to Alberta Agriculture and Rural Development, there are four basic tools in the IWM weed control tool box. • Practices that favour crop competition (e.g., seeding early, spacing rows closer together, seeding at a higher rate). • Diversified production systems that make it difficult for weeds to adapt (including perennial forages and winter cereals in the rotation). • Practices that limit the spread of weed species (cleaning combines and other equipment before moving to another field, tarping grain loads to prevent weeds from blowing out during transport). • Optimal herbicide use (reducing application rates or even skipping an application altogether). Harker, who has been talking about IWM since the early 1980s, compares it to using a series of little hammers as opposed to one big hammer. “When you combine all these things together, they can have dramatic effects even as large as herbicides,” he says. “But herbicides are so enticing.” However, that may be about to change because of a sobering discovery in Alberta last year. On January 11, 2012, Monsanto Canada issued a statement saying AAFC scientists had confirmed the presence of glyphosate-resistant kochia in Alberta. Kochia isn’t exactly the No. 1 weed problem on the Prairies. But scientists believe it may be a canary in the coal mine. Already established in parts of the United States and Australia, glyphosate resistance, if it became widespread, would be a serious problem to agriculture in Western Can-