Pea leaf weevil is on the march.
Known in southern Alberta since 1997, the weevil has grown from a minor pest to a major pain for Alberta pea growers south of the Trans-Canada Highway.
Worse, the insect is spreading rapidly.
Adults in their most extreme concentrations can damage plant growing points through feeding, but this is rare. More significant are crop losses due to larval appetites.
Larvae spend their time and get their energy from dining on root nodules.
“It’s like not having inoculated your seed and planting your (pea) crop in soil that has never seen a pea,” said Scott Meers of Alberta Agriculture.
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The larvae dine on nodules needed to fix nitrogen, which means plants fail to yield well because they don’t have enough nitrogen for growth, plant health and seed development.
Losses from larval feeding can reach 30 percent, similar to inoculant failure.
The greatest pea leaf weevil damage in 2007 was concentrated in southern Alberta near Nanton, Vauxhall, Bow Island, Medicine Hat, Magrath and Cardston.
However, economically significant levels of damage were also found north of Three Hills and east into Saskatchewan. The insect has been found at Maple Creek, Sask., and this year is expected to be found in Saskatchewan as far east and north as Kindersley.
The weevil thrives in drier, southerly areas, but Meers fears the insects’ spread will be even faster once it is fully established in the black soil zone.
“We think the higher moisture areas of the black soil zone are much more to the liking of the weevil and it will do very well there,” he said.
Unfortunately for the pulse industry, this is also where most of Western Canada’s pea crop is grown.
Insect researchers at Agriculture Canada’s research centre in Lethbridge will begin their second year of projects looking at the insect’s life cycle and how it can be controlled.
In warmer climates of the United States and Europe where pea leaf weevil is already endemic, the insect can produce more than a single generation annually. However, on the Prairies the summer provides an opportunity for only a single generation.
Adult females can lay more than 3,000 eggs, but 1,000 to 1,500 over the first two months of the growing season is more common, ensuring the larvae have a good opportunity to reach rhizobium infected root nodules, said Hector Cárcamo, who is leading the research at Lethbridge.
After dining on the root nodules, the larvae pupate in the soil and emerge as adults in late July and early August.
In the fall the adult insects move into field litter, ditches, shelterbelts and alfalfa crops.
In the spring insects are able to detect pea and fababean crops at great distances and migrate to the crop when they are weeks old. The insects will fly when temperatures are higher than 17 C but will also walk short distances. The weevils don’t appear to be interested in other pulses such as lentils and chickpeas.
Ken Coles of the Southern Applied Research Association in Lethbridge said the weevils are known to travel up to eight kilometres.
“They can find peas at great distances and migrate quickly,” he said.
