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8 Canadian experiences

In the summer of 1997 the first author of this report went on a study visit to Saskatchewan in Canada in order to learn how herbicide tolerant oilseed rape is grown in this area. The Canadian farmers can already buy herbicide tolerant oilseed rape varieties with resistance to triazines, imidazolinones, glyphosate and glufosinate, however, only the two latter are transgenics.

General

The province of Saskatchewan stretches from 49° N to 60° N but only the southern part (the northern part of the American prairie) is cultivated. The province has less than 1 million inhabitants of which 16% live on farms. The climatic conditions with cold winter temperatures do not generally allow for winter crops (only minor areas in the north or south are grown with winter wheat). Summer temperatures vary from 5 to 25 degrees Celsius, and crops are usually planted in early May, grown to maturity within 95-100 days and harvested in September. Annual precipitation varies from 324-436 mm which limits the possibilities for continuous cropping in most regions, therefore, summer fallow is common. Soil types of Saskatchewan are to the south a brown belt (stretching from north/west to south/east) with dry soils of limited quality, a black belt and a grass belt up north which are the best soils, however, this area also has the shortest growing season. Average farm size was in 1991, 436 ha of which 329 was cultivated (Saskatchewan Agriculture and Food, 1996).

Approval procedure

One of the first transgenic crops to be developed in Canada was a sulfonylurea tolerant flax (Linum usitatissimum L.) (McHughen & Holm, 1995), and the regulatory procedures had to be constructed parallel to the development of this crop. The transgenic variety must be approved by two governmental institutions: ‘Agriculture and Agrofood Canada’ who evaluates the environmental aspects and feed safety and ‘Health Canada’ who evaluates food safety. Simultaneously, the variety is being field tested as other future varieties, and the results from two to three years of trials are evaluated by the ‘Prairie Registration Recommending Committee’.

The Saskatchewan canola area (Table 8.1) accounts for approximately 50% of the Canadian canola area and, for comparison the Danish area with oilseed rape is 152[ 10³ ha (Miljøstyrelsen, 1996). Canola is divided into ‘Argentine canola’ (Brassica napus) and ‘Polish canola’ (Brassica rapa). Polish canola needs fewer days to mature and is grown in areas where either precipitation is low or the season is short. Currently, there are no transgenic varieties of this species on the Canadian market.

Crop rotation

The typical canola rotation is a four year rotation to prevent disease problems:

Weeds

The fields inspected on this study visit were infested with Thlaspi arvense L. (Stinkweed), Sinapis arvensis (Wild mustard), Descurainia sophia L. Webb (Flixweed), Lactuca serriola L. (pricly lettuce) and/or Avena fatua (wild oats).

Main crops

Table 8.1

Traditionally trifluralin alone or in a mixture with ethalfluralin has been used to control weeds pre-emergence. The first application comes in the autumn and the second in spring . Approximately two out of three farmers will use an autumn application to get high efficacy and then spot spray post-emergence with an aryl-propanoic acid or cyclohexanedione herbicides for grass weeds, and ethametsulfuron methyl (an ALS-inhibitor) with 15-23 g a.i. ha^-1 for control of Sinapis arvensis, and clopyralid for control of thistles. In the cereal crops, the farmers can use a variety of herbicides, e.g. herbicides with auxin activity are available, in contrary to Danish conditions, and 2,4-D is an efficient option to control volunteer rapeseed. Otherwise a mixture of bromoxynil and MCPA is often chosen. ALS-inhibiting herbicides are seldomly used because of residual activity in the soil in the succeeding dicot crop (low temperatures and short seasons). The management system is slowly moving towards a no till system which relies on pre-emergence glyphosate applications for weed control followed by direct seeding of the crop.

Agronomic benefits

Herbicide resistant oilseed rape allows for post-emergence weed control and do not have to be incorporated into the soil which reduces risks of soil erosion and evaporation of soil moisture. With the traditional herbicides farmers often have to wait seeding the crop until herbicides have been incorporated into the soil, which in an area with a short growing season can be costly if early frost kills the crop (immature oilseed rape contains chlorophyll which can reduce crop value by 60%). If the problem is grass weeds, then the farmer will most likely prefer glyphosate tolerant oilseed rape, however, if wild mustard is a problem an imidazolinone resistant variety is preferable. Glufosinate is intermediate glyphosate and imidazolinones in efficacy. Farmers are not likely to use the same resistance mechanism in the next canola crop, that will depend on weed problems and seed/herbicide costs.

Herbicide tolerant varieties

Table 8.2

Seed price

Glufosinate is patented by AgrEvo, and the company covers the costs of developing the transgenic varieties by the increased sale of the herbicide. Glyphosate is off patent, therefore, Monsanto signs a ‘technology use agreement’ with the farmer before the farmer buys glyphosate tolerant seeds. This contract costs 37,5 CAD ha^-1 and furthermore restricts the farmer not to use the harvested seed for a new crop. Once the agreement is signed, the farmer will go to the grain company and buy the seed, as normally; so the contract is the costly part.

Farmer survey

Monsanto sent a questionnaire to 289 farmers who had grown glyphosate tolerant oilseed rape in 1996. The majority of these farmers had sprayed once with glyphosate with 445 g a.i. ha^-1 at the 3-4 leaf stage of the oilseed rape. A comparison was made between 31 of these farmers and 31 farmers with similar conditions growing non-transgenic oilseed rape varieties, and the net result was an average incremental return of 65 CAD ha^-1 (Monsanto, 1997).

Restrictions

There are no restrictions to the farmers management of the transgenic oilseed rape crops. However, the plant breeders must use a 10 m wide pollen catching belt of oilseed rape crop around the transgenic breeding material or 50 m distance to the nearest oilseed rape crop.

Hybrid systems

The hybrid-liberty system refers to a transgenic oilseed rape where pollen sterility is combined with glufosinate tolerance. It was developed by Plant Genetics Systems which is now part of AgrEvo. The system, which is not yet available to the farmer, allows for yield increases around 15-30% compared to normal free pollinated varieties. Glufosinate is used in the seed production to select for transgenic plants, but the farmers are likely to use the trait agronomically by spraying with glufosinate in the commercial production. AgrEvo will probably move the breeding programme towards this system. Other non-transgenic hybrid systems which uses cytoplasmatic male sterility can also be used to obtain hybrids, however the cytoplasmatic male sterility systems are more susceptible to environmental effects which can reduce the number of hybrid plants obtained (AgrEvo, 1997).

Concerns

In a minimal tillage situation, the farmer is dependent on glyphosate used pre-sowing to control weeds. Furthermore, glyphosate is used to control weeds in summer fallow. There is to date, however, only one occurrence of weed with increased tolerance to glyphosate, which is a biotype of Lolium rigidum from Australia (Heap, 1997).

Resistance to ALS-inhibitors is well-known in the Saskatchewan area and when farmers grow non-transgenic imidazolinone tolerant oilseed rape this will increase the selection pressure towards weed with resistance to these herbicides. However, Canadian farmers probably have less tradition for using ALS-inhibitors in the cereal crops compared to Danish farmers, which may delay the occurrence of resistance in weeds.

Conclusion