A ravenous grey insect is chewing its way across Alberta canola fields.
The cabbage seedpod weevil, an immigrant from the northwestern United States, has been found in fields across southern Alberta. Recent reports of sightings have also come in from Maple Creek, Sask., but scientists in that province are hoping to contain the problem.
In Alberta, the problem has grown beyond containment.
“We’re in the middle of the weevil wars right now,” said Jack Payne, crop specialist with fertilizer company Westco in Taber, Alta.
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The insect has been discovered in the buds of canola plants. Insects chewing through the buds will cause blasting and prevent flowers and pods from forming.
Farmers are advised to sweep fields with a net in a 180 degree arc. It is time to spray if 10 sweeps catch 30-40 weevils. An emergency registration for the insecticide Decis has been approved in Alberta. Lorsban and Matador have also applied, but they may not be ready this season, said Payne.
Farmers are advised to spray from the bud stage to early flowering.
“We’re spraying now because once the egg is inside the pod, no insecticide is effective,” Payne said.
He recommended checking sprayed fields a week later to make sure the weevils are killed.
In Saskatchewan control measures are less urgent.
“It is in a fairly isolated area in southwestern Saskatchewan,” said provincial agriculture entomologist Scott Hartley.
“It has not been found north of the South Saskatchewan River. We know it has been found in crop samples taken around Maple Creek and in the Golden Prairie area.”
Hartley is hoping that producers and scientists can confine the insect to the southwestern area. He wants to establish an eastern boundary south of Highway No. 1.
“It would have to make a significant leap to get out of the traditionally non-canola growing area in the southwest into the major canola growing area running from the north- west to southeast part of the province.
“It has the Great Sandhills and large expanses of rangeland to cross that are not going to be conducive to the beetle biology and life habits.”
Hartley said the numbers in Saskatchewan do not yet warrant control measures. The insect is highly mobile and can fly up to five kilometres.
Weevils are believed to overwinter in ditches and shelterbelt trash. They can feed on stinkweed and wild mustard and move into a field from the edges. Weevils seem to be attracted to the color yellow so early canola blooms lure them into the field.
The cabbage seedpod weevil is approximately four millimetres long, ash-grey in color and has a prominent curved snout typical of the weevil family of beetles.
The adult female lays between 60-100 eggs in newly formed canola pods. The eggs hatch within a week starting in mid-June.
The larva is three or four mm long and is white with a dark brown head. Legless and grub-like in appearance, the larvae feed on developing seeds within the seedpods. Larvae-infested pods are subject to shattering.
Mature larvae chew small, circular holes in the walls of the pods, drop to the soil, burrow in and pupate. Adults emerge about 10 days later and feed on canola until late in the season when temperatures drop. They remain dormant over the winter.
The last two mild Alberta winters may have helped them survive.
The weevil first appeared about five years ago and has spread rapidly because of few controls.
“They have spread very significantly,” said Payne.
“We suspect they will be able to colonize the entire canola crop in Western Canada.”
