The Municipal District of Bonnyvllle is killing off the noxious weed, Canada Thistle, one weevil at a time. Our goal is to rid our natural pathways of this prickly, spiny plant as well as to protect our native habitat.
Canada Thistle is a highly competitive weed that occurs in a wide range of habitats. It is listed as “noxious” under the Alberta Weed Control Act. That means these weeds must be controlled, which is difficult to do. Its root system can extend up to six metres underground and 4.5 metres horizontally. This plant also produces up to 1,500 seeds, which are dispersed by wind, and can remain in the soil for up to 20 years. Dense riparian infestations can impact wildlife by outcompeting native plants (food) and nesting cover for waterfowl.
Chemicals and cultivation cannot be used on the M.D.’s Environmental Reserves located around our lake areas. This is to protect the wildlife, birds and the aquatic ecosystem. That’s why the M.D.’s Agriculture and Waste Department is doing a trial with Canada Thistle Stem-Mining Weevils.
These weevils are non-invasive, do not bite, and are slow moving. They restrict their feeding to thistle and a few close relatives to this weed making it a natural choice for biological pest control. They have been approved as a biological control in Canada since 1965.
So how does it work?
In the spring the larvae internally mine inside the stem of the thistle plant. They emerge later in the summer to feed on thistle leaves before winter. The adults then, over the winter, sleep in the soil and attack the emerging thistle in the spring. When the larvae mine the stem, they consume the plant tissue leaving a hole, which allows other micro-organisms to enter the plant with adverse consequences for the thistle.