While scouting a canola field for lygus bugs two years ago, Rod Lanier came across a pest insect he had never before seen on his farm.
The insect, the cabbage seedpod weevil, had migrated into his field from a nearby highway where canola plants served as a cover in ditches.
“The edge of our field was just thick with them,” recalled Lanier, who farms south of Lethbridge, Alta.
The cabbage seedpod weevil returned to his canola crops last year, and high counts of the insect were recorded again in 1999.
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Lanier now is waiting to learn how much profit the weevil has eaten.
“It would really concern me if we saw huge damages, but I don’t think we did.”
Lloyd Dosdall, a research entomologist with Alberta Agriculture, said the cabbage seedpod weevil has spread across most of southern Alberta.
It was first detected there in 1995.
“In four years, it’s increased dramatically,” said Dosdall.
“It’s a threat now to the main area of canola production in Alberta.”
Yields losses in the Taber area this year ranged anywhere from one percent to 30 percent.
The weevil’s larvae spend three to four weeks in the pod, consuming five to seven canola seeds each.
When they finish feeding, the larvae chew exit holes at the base of the pods and drop to the ground to pupate. The adults emerge two to four weeks later to feed on green stems and ripening canola pods.
Entered in B.C.
The cabbage seedpod weevil traveled to Canada from Europe in the 1930s. It was first noted on British Columbia’s southern mainland, where it attacked broccoli, cauliflower and cabbage.
It eventually spread to Washington state and Oregon and now affects much of the canola grown in the United States.
The menacing insect has yet to appear in Saskatchewan and Manitoba canola fields. The outlook for Alberta is not so encouraging.
“We’re seeing enormous numbers going into overwintering this fall,” Dosdall said. “Those numbers are a way higher than they were in 1998.”
Researchers are gathering the data needed to get pesticides registered to combat the cabbage seedpod weevil in Canada. Natural enemies are also being sought and researchers are looking for canola varieties that are less susceptible.
“It’s a pretty tough little insect,” said Dosdall. “I think the next couple of years will tell the tale about it.”
Lanier hopes catch strips of fall-seeded canola will help reduce weevil numbers next year. The fall-seeded strips should blossom earlier than the rest. He hopes the weevils, attracted by the yellow flowers, will converge on those strips where they can be killed with a pesticide.
