Critical Thinking

Wild agricultural crops in the Canadian prairies (Friesen

Wild
mustard (Sinapis arvensis) is prevalent weed that is found widespread
throughout Canada and north central United States (Christoffers et al., 2006).
Considered to be native to Europe, the Middle East and western Asia, reports of
wild mustard populations in western Canada go back as far as 1860 in Fort
Garry, Manitoba and 1875 in Dufferin, Manitoba (Mulligan and Bailey, 1975).
Since then, wild mustard has become an important weed of agricultural crops in
the Canadian prairies (Friesen et al., 2009; Warwick et al., 2005).
In 2003, wild mustard was ranked 15th out of 124 weeds in a
Saskatchewan survey of cereal, oilseeds, and pulse crops (Leeson et al., 2003)
and 11th of 101 weeds in a 2002 survey of cereal and oilseed crops
in Manitoba (Leeson et al., 2002).

Wild
mustard is a broad-leafed annual weed species with indeterminate growth (Warwick et al., 2000).
It is self-incompatible, grows in locations with high light intensity and is
readily killed by frost (Warwick et al., 2000).
Wild mustard can be easily identified by several of its distinguishing
features. This includes kidney shaped cotyledons; coarsely hairy stems with
petiolate lower leaves and sessile upper leaves; bright yellow, four-petalled
flowers; pods are generally hairless and terminated by a flattened beak; valves
split lengthwise at maturity; and the seeds are black-purplish (Mulligan and Bailey, 1975).
Often confused with several yellow-flowered annuals, such as Brassica rapa,
Brassica napus, and Sinapis alba, Wild mustard is distinctive from theses as in
addition to having seeds within the valves, there is also seed in the beak of
the pod (Warwick et al., 2000).

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Wild
mustard is a potentially very problematic weed within the Canadian prairies.
Due to its high reproductivity, competitive growth habit, and persistent seed
bank, the yield loss of agriculture field crops can become serious. For
example, in spring rapeseed, yield can be reduced by 20% with population
densities of wild mustard being as low as 10 plants per m-2 (Buchanan,
2016). Although there are many available herbicides to control wild mustard in
field crops, biotypes of wild mustard resistant to Group 2, Group 4, and Group
5 herbicides have been reported in Canada in the 1980s and 1990s (Warwick et al., 2000).
Acetolactate synthase (ALS) inhibitors (Group 2) resistant wild mustard was
initially discovered in Manitoba in 1992 (Morrison and Devine, 1994)
and was later discovered in 2002 in Saskatchewan (Warwick et al., 2005).

Kochia
(Kochia scoparia) is one of the most prevalent summer annual broadleaf weed. It
is located throughout Canada, except for the maritime provinces and coastal
British Colombia (Royer and Dickinson, 2006).
Initially categorized as rare in Saskatchewan and Alberta in 1948 (Friesen et al., 2009),
kochia was the 10th most prevalent weed across the Canadian prairies
(Leeson et al., 2005). Kochia is present in 13% of surveyed Canadian prairies
fields, and is most common in Saskatchewan (8th in Provincial
ranking) occurring in 17% of fields with a mean density of 4.2 plants m-2
(Friesen et al., 2009).

Kochia
is described as a bushy, pyramid-shaped plant with potential to reach heights
of 2m (Royer and Dickinson, 2006).
Kochia has a potentially large tap root (up to 5m long) and its stem is erect,
branched, green or red tinged, and can somewhat be hairy (Friesen et al., 2009).
It has a high tolerance of saline soils (Friesen et al., 2009),
early emergence, and low seed dormancy (Kumar and Jha, 2015).
It is also an abundant seed producer, were a single plant will produce more
than 14,000 seeds (Schwinghamer and Van Acker, 2008).

Kochia
has built up resistant to several modes of action including acetolactate
synthase (ALS) inhibitors. Group 2 resistant kochia was first discovered in
Saskatchewan and Manitoba in 1988 (Morrison and Devine, 1994).
Due to its tumbleweed mobility and ability to cross pollinate, populations of
group 2 resistant kochia has become increasingly common. In 2007, Beckie et al.
found that 90% of the 109 prairie fields surveyed, had widespread resistance to
ALS inhibitors (2013).
This increased spread of resistant kochia may be in part caused by transmission
through pollen movement, however seed dispersal by mature plants moving through
the prairie landscape is likely responsible for the long-distance transport of
group 2 resistant kochia (Beckie et al., 2016; Hall et al., 2014; Stallings et
al., 1995).
Although the spread of group 2 resistant kochia is difficult to prevent,
management practices including crop rotation (Government of Saskatchewan, 2017)
and rotation of broadleaf herbicide (Government of Manitoba, 2015) should be
used to delay the development of ALS inhibitors resistance.

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