178 – II.3. BRASSICA CROPS (BRASSICA SPP.)
with cereals. Wheat yields following a B. napus crop invariably improve in Europe and
Australia due the reduced level of cereal pathogens present and the control of grassy
weeds (Almond, Dawkins and Askew, 1986).
North and South America
The oilseed rape/canola grown in North America is concentrated in the northern part
of the Western Great Plains (Figure 3.26). The species and form grown is almost
exclusively the spring or annual B. napus. In western Canada, less than 1% of the
5 million ha is sown to spring B. rapa. Production of the winter or biennial form of
B. napus in North America is confined to a few thousand hectares in the Province of
Ontario, Canada and a few west and central states in the United States. In South America,
both spring and winter B. napus is produced on some 17 000 ha in central Chile.
Figure 3.26. Areas of oilseed rape/canola production in North America
Notes: Light grey indicates heavier production concentration.
Source: Courtesy Canola Council of Canada.
Cultural practices in the main oilseed rape production regions of western Canada and
the United States have changed in recent years. Traditionally the crop was sown into
summer fallow, land laid fallow the previous year. With the shift to continuous cropping
and minimum tillage, B. napus is now sown into the undisturbed stubble of the previous
year’s cereal crop. Weed control, which would normally be a problem with this direct
seeding system, can now be easily achieved with the new broad spectrum,
post-emergence herbicides such as glyphosate, glufosinate and the imidazolinones. The
adoption of these herbicides and their associated herbicide resistant varieties has been
extremely rapid (Figure 3.27).
