II.3. BRASSICA CROPS (BRASSICA SPP.) – 175
GM HR canola compared to conventional varieties. Furthermore, prior to any field
operations, they found an average over all fields of 200 volunteers/m^2. Initial soil
disturbance was effective in controlling these emerged B. napus volunteers, but shallow
cultivation resulted in the emergence of an even greater number of volunteers.
A post-emergent weed control programme employed by the producer for the non-GM
volunteers was also effective in controlling the GM volunteers (MacDonald and Kuntz,
2000). Downey and Buth (2003) reported that GM HR volunteers with single or stacked
traits were readily controlled in western Canada by the same agronomic practices that are
standard for controlling conventional canola volunteers. In Australia, post-harvest
monitoring of GM HR (glufosinate or glyphosate) trial locations for six years indicated
volunteer populations were adequately controlled by herbicide application or broadacre
cultivation (either in-crop or by conservation tillage) (Salisbury, 2002).Figure 3.25 Approximate areas of the phytogeographic regions containing the world’s greatest
representation of Brassicaceae genera
Note: They encompass the Mediterranean (black); the Irano-Turanian (striped) and the Saharo-Sindian
(dotted) regions.
Source: After Hedge (1976).Feral populations of B. napus can be found at various densities on road verges, along
field margins and railway lines in all countries where it is grown (e.g. Crawley and
Brown, 1995; Wilkinson et al., 1995; Squire et al., 1999; MacDonald and Kuntz, 2000;
Agrisearch, 2001; Pessel et al., 2001; Orson, 2002; Salisbury, 2002). Populations may
also become established in port areas where B. napus cargos are handled (Ramsay,
Thompson and Squire, 2003; Saji et al., 2005; Aono et al., 2006). Annual recruitment to
such sites is likely to be more from passing transport vehicles than from an established
seed bank. B. napus, as with other Brassica species, is a coloniser of disturbed soils
where it competes with other primary colonisers. However, B. napus is a poor competitor
and is not regarded as an environmentally hazardous colonising species (European
Commission, 2000, 1999, 1998a, 1998b; Beckie, Hall and Warwick, 2001; Dignam,
2001). Unless the habitats are disturbed on a regular basis, B. napus will be displaced
(OECD, 1997).
In western Canada, roadside verges, field margins and railway lines were surveyed
for canola plants (MacDonald and Kuntz, 2000). Only 13 and 27 volunteer B. napus
plants were found in the mowed roadside over the respective 7 and 27 kilometres
surveyed, and no plants were found in tall, unmowed grass. Surveys of rail beds leading