Pulse School: Pea leaf weevil's range expanding east

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First found in Canada in southern Alberta in the 1990s, the pea leaf weevil is continuing to expand its territory to the east.

The invasive pest whose larvae feed on the rhizobia in nitrogen-fixing root nodules has since spread across most of the pea-growing areas of Alberta and Saskatchewan. It was first detected in Manitoba, in the Swan River Valley, in 2019.

“Last fall we did a big survey push going into those pea crops post-harvest, we collected some weevils, and we confirmed that they’re pretty common in western Manitoba,” says Laura Schmidt, production specialist with Manitoba Pulse and Soybean Growers, in this Pulse School episode.

If it wasn’t already, agronomists and producers in southwest and central Manitoba should have pea leaf weevil and the telltale hole-punch leaf notching that it causes on their radar.

“Based on some climate modelling across the Prairies, Manitoba falls in the favourable to very favourable category. So while population numbers have been declining in Alberta and Saskatchewan from the dry weather, we’ve got lots of moisture to work with here in Manitoba. We’re likely to see this population increase a little bit. So we want to keep an eye out.”

As of this summer, pea leaf weevil’s presence was confirmed “pretty much anywhere west of Highway 34 in Manitoba,” says Schmidt. “If we’re in the central region, and we’re seeing leaf notching, that’s where we want to give myself or [Manitoba Agriculture entomologist] John Gavloski a call so we can get some more information. Have we seen an expanded range? Or is this one of the other weevil species that we’re not so concerned about?”

There are foliar insecticides registered for pea leaf weevil, but Schmidt says they can be ineffective for several reasons: adults that are controlled by spraying have already laid eggs, and there can be multiple migrations into a field.

An insecticide seed treatment can be a more effective control option, she says, as it can delay larval development; but at the same time, Schmidt says there may not be an economic return on using a seed treatment.

A trap crop, such as faba bean, which stays green a later into the season than peas, is also an intriguing concept, she says. “Once that pea crop comes off and is harvested, all of those newly emerged, adult weevils would move into that strip of faba beans…And then you could control them when they’re all concentrated in that faba bean strip before they moved to overwintering sites.”

Check out the Pulse School video above — filmed at the 2022 Manitoba Crop Diagnostic School — for more on pea leaf weevil’s move east, how to scout for the pest, and potential options for managing it.

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