There are many different types of invasive plant species,
often referred to as "weeds" that cause problems for agriculture
producers in Alberta. Some of the more important plant species include Canada
thistle, chickweed, cleavers, flixweed, scentless chamomile, stinkweed,
toadflax, narrow-leaved hawk's beard and wild oats. These weeds can be highly
competitive, particularly if they become established before the crop. Wellestablished weeds compete with the crop for soil moisture and nutrients. The
more severe infestations can reduce yields drastically, and can constitute a
significant economic loss to the farmer. For example, a light infestation of
only six Canada thistle plants per square metre reduce wheat yields by 18 percent,
whereas a more typical infestation of 24 plants per square metre can reduce yields
by 61 percent.
Tillage used to be the principal means of controlling
invasive plant species on cropland in Alberta. However, changing land management
practices have seen a trend toward less tillage of the soil, and reductions in
the amount of summerfallow acreage. With the availability of modern—day
herbicides, weed control in the agricultural sector has shifted dramatically
towards chemicals combined with other control methods.
In recent years, the number of herbicide-resistant weeds
and the area they infest in western Canada has increased at an alarming rate.
Much of Alberta's crop area is in the early stages of one type of resistance or
another. Weed resistance to a particular herbicide arises through natural
selection following repeated use of the herbicide for a number of years on the
same field. The best methods to delay establishment of resistant weeds include
regularly changing crops and herbicides, and using plant competition, mechanical
methods, and other means to augment chemical control.
Department of the Environment. State of the Environment Report, Terrestrial Ecosystems. Edmonton: n.p., 2001. With permission from Alberta Environment.