Doug Moisey was checking canola in a southern Alberta test plot last summer when something caught his eye – a pod with a hole in it.
“It was kind of curled, and it looked anorexic on one side, very thin. And when I opened it up there was this little worm staring back at me, sticking out from one of the canola seeds,” said the Canola Council of Canada agronomist.
This was Moisey’s – and Canada’s – first recorded look at the cabbage seedpod weevil.
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The weevil was first discovered in Alberta by an American scientist checking plots in the fall of 1995. “It wasn’t till the spring of ’96 that he happened to tell anybody here about it,” said Mike Dolinski, an Alberta Agriculture entomologist.
Survey done this year
“We found, by sheer luck, a few specimens last year, in ’96, and this year we actually did a southern Alberta survey.”
Results localized the problem in the area south of the Trans-Canada Highway.
The weevil has not been found in Saskatchewan or Manitoba.
Cabbage seedpod weevils have caused high losses in the U.S. Pacific Northwest and in Europe.
“From what I’ve been told, is that left unchecked in high enough populations, it’s in the vicinity of 20-30 percent losses,” Moisey said.
So far, numbers aren’t high enough to do significant damage, but there are some hot spots.
“Some of the fields I sampled south of Lethbridge had population levels that were approaching the economic threshold (for spraying) that’s used for this pest in the United States and Europe,” said Lloyd Dosdall, of the Alberta Research Council. “To me, it’s reason for serious concern.”
The ash-grey adult weevil measures about 2.5 to three millimetres, overwinters under litter and beneath the surface in light soils and emerges in spring to lay eggs.
Eggs are usually laid singly at one end of the pod. Females can lay up to 150 eggs.
The larvae spend three to four weeks in the pod, and do the most damage to crops. Each larva eats five to seven canola seeds on one side of the septum before chewing a hole in the pod and dropping to the ground to pupate. When the host plants mature, the weevils go into hibernation close to the previous host plant location.
Winter and early spring seeded canola provide an ideal host for the weevil, because it can start eating sooner in the season. The recent trend toward fall-seeded canola could provide additional hosts, because the crop would be up even earlier.
May reduce pollination
In the U.S. the pests are sprayed, but Dolinski wants to avoid that, in order to protect bees and other pollinators. The canola has to be sprayed “in the mid to late part of bloom, which is really a nightmare from a pollinator risk perspective.”
He said an alternative is importing several parasites from Idaho or Europe which feed on the adult and larva forms of the weevil. So far, numbers are low enough to warrant the watch and wait approach.
“We would probably want (a farmer) to report it to his local district specialist so we could keep a handle on how it’s spreading,” Dolinski said.
The weevils can be seen on canola blossoms, but holes in the pods are the most obvious sign.
All research on the weevil has been done on winter canola in the U.S. and Europe.
“We really don’t know how well it can complete it’s life cycle on spring canola, and we hope to study this in the forthcoming years,” said Dosdall.
Dolinski is optimistic.
“I don’t honestly believe because of the type of canola we grow here and our pretty harsh environmental conditions (that the weevil can survive.)”
