Genetically modified oilseed rape in Canada: Taking stock after ten years of cultivation

Although genetically modified oilseed rape is not yet grown in Europe, it now accounts for just under 90 percent of the total oilseed rape production in Canada, the world’s largest exporter of rape. The acreage under rape cultivation in Canada has been increasing steadily since it was first approved in 1995. Improved weed management, increased yields and fuel savings were the decisive factors persuading farmers to switch to the new GM varieties. According to reports from farmers and environmental organisations, ‘GM-free’ conventional and organic oilseed rape cultivation has virtually disappeared in Canada.

Whilst in Europe a debate is still raging about the coexistence ability of GM crops, and of oilseed rape in particular, in recent years the majority of Canadian farmers have opted in favour of growing GM rape. According to Statistics Canada, rape production has increased from 4.5 million tonnes per year to 9.1 million tonnes (2006) since genetically modified varieties were introduced in 1996. The Canola Council of Canada wants to increase production to 16 million tonnes by 2015, with oil and biodiesel production in North America and Europe being the most important sales markets.

Oilseed rape cultivation in Canada: Vigorous growth. Genetically modified varieties have now been adopted throughout almost the entire country.

Proportion of different herbicide-resistant systems in oilseed rape varieties in Canada. Breeding programmes for herbicide tolerance have a long history. In 1981, long before the introduction of genetically modified varieties, conventionally bred triazine-tolerant canola varieties were available. However, these varieties never achieved significant market relevance due to their low yields and are now no longer available. Bromoxynil-tolerant oilseed rape, another conventionally bred herbicide-tolerant rape, although still listed in the range of varieties, no longer has any market relevance.

Widespread adoption of herbicide-tolerant oilseed rape

Herbicide-tolerant rape is currently grown on more than 95 percent of the area under rape cultivation in Canada. In addition to varieties with genetically engineered resistance to the active substances glyphosate (trade name Roundup) and glufosinate (trade name Liberty), conventionally bred herbicide-tolerant oilseed rape is grown on around 9 percent of the area under rape cultivation. This Clearfield oilseed rape is tolerant of the active substance imidazolinone, a broad spectrum herbicide. Following initial market success, Clearfield technology has been largely eclipsed by the genetically modified RoundupReady and Liberty Link oilseed rape varieties in recent years. There is now virtually no demand for oilseed rape varieties without herbicide tolerance. Organic rape cultivation, which has always extremely marginal, accounted for around 0.04 percent of the rape cultivation area in 2003.

A survey of farmers conducted by the Canola Council of Canada showed that simple and effective weed management is the most important reason for growing herbicide-tolerant GM oilseed rape. The new system enables farmers to tailor herbicide use to actual weed presence in a flexible way.

The successful market penetration of herbicide-tolerant GM varieties is due largely to the fact that new high-performance hybrid varieties were used. Yields are up to 10 percent higher than those obtained from conventional varieties.

Coexistence, a matter of concern?

Unlike in Europe, the ability of GM oilseed rape to coexist alongside conventional crops was not considered to be a controversial issue in Canada for quite some time. In just a few years, herbicide tolerant GM varieties became the cultivation standard. For no other crop and in no other region has market penetration been so successful.

In Canada there are no special labelling regulations for food and fodder containing GMO presence. The harvest from GM and non-GM oilseed rape is marketed together. No minimum separation distances between fields of GM and conventional oilseed rape are required.

Improving seed production regulations

It was not until conventional rape seed was found to be contaminated with genetically modified seed that a serious debate was launched to determine whether the existing technical regulations were sufficient to guarantee the purity of conventional seed.

Genetic impurities of up to 5 percent have been identified in individual batches of certified, conventional seed in recent years. There are now plans to revise the regulations to maintain the guaranteed 99.75 percent purity of certified seed. For example, an increase in the separation distance from neighbouring oilseed rape fields in seed production, which currently stands at 100 metres, has been proposed. However, according to Hugh Beckie, research director and expert on oilseed rape management at the Canadian Ministry of Agriculture in Saskatoon in the province of Saskatchewan, the possible contamination of conventional rape seed via seeds from GM oilseed rape volunteers is of far greater concern than incrossings via GM pollen. The idea of shifting seed production to Canada’s south-western provinces, well away from the main production areas for oilseed rape, is therefore also under discussion.

Organic farmers dissatisfied

In 2002 a group of organic farmers from Saskatchewan filed a complaint about the cultivation of GM oilseed rape, thus focussing attention on the issue of liability for GMO presence in conventional harvest products. Arnold Taylor, President of Canadian Organic Growers, believes that the coexistence of genetically modified and conventional oilseed rape in Canada has been a failure. Farmers now had no other choice but to market the entire oilseed rape harvest as genetically modified. In spring 2007, after a legal battle spanning several years, the Supreme Court of Canada decided not to admit the claim for compensation for economic losses as a result of GMO contamination. And so the question of liability remains unresolved for organic farmers.

All clear: no problems with ‘herbicide-tolerant rape volunteers’ so far

Volunteer oilseed rape is a major weed, emerging in fields and, in greater numbers, in field margins. With the increasing cultivation of GM oilseed rape, there have been concerns that ‘super weeds’ could develop: weedy rape with multiple herbicide resistances which could no longer be controlled by conventional means. And yet so far, herbicide-tolerant volunteer rape has not become a major problem in farming. In questionnaires conducted in 2000 and 2005, three-quarters of farmers growing herbicide-resistant oilseed rape stated that controlling volunteers in genetically modified oilseed rape was no greater problem than in conventional oilseed rape. They did not need to use more spray, neither did they incur higher costs. Cereal crops are generally grown in rotation with oilseed rape. Herbicide-tolerant oilseed rape volunteers can easily be controlled with the herbicides used on cereals.

When genetically modified oilseed rape was first introduced in Canada, there were no post-release monitoring programmes to prevent the spread of resistant volunteers. However, since 2004 each new approval requires a stewardship plan, which must take into account such factors. In recent years, corresponding stewardship plans have also been developed on a voluntary basis for GM oilseed rape varieties approved before 2004. Forward-looking management strategies to reduce multiple herbicide-tolerant volunteer rape are now regarded as a high priority. Some of the key preventative measures that have been introduced include adapted harvesting techniques such as post-harvest tillage, appropriate crop rotation, the cultivation of certified seed and wherever possible no simultaneous contiguous cultivation of varieties with different herbicides tolerances.

New herbicide-resistant weeds – only a matter of time?

So far no weed species resistant to the herbicides glufosinate or glyphosate have been found in Canada. The special mode of action of glufosinate makes resistance formation appear highly unlikely. Despite several years of intensive use, no resistant weeds have yet emerged anywhere in the world. The picture is rather different for glyphosate: in 2000 the first glyphosate-resistant weeds emerged in GM soya. Since then, there have been reports of other herbicide-resistant weed species in intensive GM maize and GM soya crop rotations. If the same crop is grown in succession, it will be only a matter of time before weeds become resistant to the herbicides used.

By contrast, Canadian GM summer oilseed rape requires an alternating cereal-oilseed rape crop rotation, which allows the active substances used in weed management to be rotated. The lower selection pressure compared with GM maize or soya crop rotations is thought to be crucial in explaining why no glyphosate-resistant weeds have yet emerged.