WINNIPEG – Researchers are looking to nature for an answer to one of the most persistent and problematic weeds around – Canada thistle.
As early as this year, several species of Chinese insects could be released into fields to see if they’ll do the trick on the weed and survive cold Canadian winters.
This is Canada Thistle Week, named by weed specialists and the chemical industry on the Prairies for a weed that has had the ideal habitat to thrive and multiply.
Carla Allen, a weed specialist in Manitoba who is also in charge of the province’s biological control program, said thistle loves wet conditions, and for the past few years there have been field-wide infestations of the weed. In fact, half of all the fields in Manitoba are home to some thistle.
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Weed control strategy
Allen said farmers need a three to four-year strategy to control the weed, including spraying at different times and planting competitive crops.
Insects may become part of the strategy. Various groups across the Prairies, including the Manitoba Weed Supervisors Association, are contributing to a three-year project using bugs on Canada thistle. Peter Harris, a scientist at the Lethbridge Research Centre, is co-ordinating the work and has spent the last year finding and screening species.
Allen said Harris traveled to northern China, which has a similar climate to Western Canada, to talk to scientists about insects that feed on thistles. Then, he screened several species to find out if they would attack or harm other plants, or attract other pests to fields. Some of the insects eat the leaves or seed heads of the thistle. Others mine the stems of the weed or attack the roots.
“They’ll only be successful if they can acclimatize or adapt to our climate,” said Allen. “If the environment or climate that they come from in China is as close as we think to Western Canada, they look promising.”
Like other insects, they spend the winter as pupae in the soil, and emerge as adults in the spring.
Researchers will try confined field releases this year or next, depending on final approval. Allen said insects would likely be placed in a cage in a thistle patch so they could be monitored.
Manitoba’s biological program has worked on nine different weeds using 12 different insects. Allen said the program has had good results, particularly with leafy spurge insects.
