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Part of Cabbage seedpod weevil

Cabbage seedpod weevil – Survey and maps

Results from recent and past cabbage seedpod weevil survey work across Alberta.

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Cabbage seedpod weevil

This is not a forecast. It is a summary of the situation in Alberta in the summer of 2025.

Methodology

The 2025 survey covered the canola growing areas of southern and central Alberta. 257 fields in 51 municipalities were sampled in late June to early July when canola was at 20 to 25% flower. Surveyors sample by taking 25, 180 degree sweeps through the crop starting at the field edge and walking toward the centre of the field.

2025 survey findings

Map of Alberta showing the number of cabbage seedpod weevils per 25 sweeps found in the 2025 survey. This map uses a six color gradient from light green (0 weevils) to red (more than 90 weevils). The areas south of Lethbridge and around Medicine Hat are dark red and gradually decrease through orange and yellow further North towards Edmonton. There are small pockets of dark orange and dark red to the northeast of Calgary and around Red Deer. Individual survey points with dark green are found as far North as

Cabbage seedpod weevil survey map 2025

Cabbage seedpod weevil was found in high numbers in the 2025 survey. The survey found the weevil above economic levels in southern Alberta as well as into central Alberta. Numbers of weevils were particularly high in the Highway 3 corridor but were not confined to distinct hotspots.

In 2026, it will be important to scout for cabbage seedpod weevil across the south and central regions. Scout canola when in early flower, especially those first to flower fields, to make control decisions. If control is warranted, make sure to follow economic thresholds and best management practices to protect pollinators.

In 2025, we found weevils above economic levels as far north as Red Deer County, which is unusual. Individual weevils were found as far north as Yellowhead County. These counts were well below threshold, but this is farther north than we usually see the weevil.

Agriculture and Agri-Food Canada at Beaverlodge conducts the canola survey in the Peace River region where no cabbage seedpod weevils have yet been found.

Cabbage seedpod weevil overwinters as an adult, so the risk of infestation is further indicated by the adult population of the preceding fall. High numbers of weevil adults in fall will likely mean significant infestation levels in the following spring. This map does not adjust for the emergence of the new generation in the fall or overwintering conditions. Favourable weather conditions for the new generation of weevils may lead to higher numbers in the following year. These conditions include cooler temperatures and rainfall in August and mild winters with a heavy snowpack.  

The cabbage seedpod weevil takes roughly 8 weeks to develop from egg to adult. Development time will vary somewhat depending on weather conditions, especially temperature. There is one generation per year. Follow this link for further information about the life cycle.

Crop damage from cabbage seedpod weevil can occur from:

  • larval feeding within developing pods (larva consumes 5 to 8 seeds, this is the major source of losses)
  • premature shattering of damaged pods
  • new generation adults that emerge in the fall feeding on nearly developed seeds (usually concentrated only on very late crops).
  • bud-blasting (potentially reducing yield in dry years though not experienced in Alberta)

The larval feeding can result in yield losses of 15 to 20% in each pod infested.

Cabbage seedpod weevil adult abundance is best monitored by using a sweep net. Sampling should begin when the crop first enters the bud stage and continue through the flowering period. Select 10 locations within each field, and at each location count the number of weevils from 10, 180 degree sweeps. Sampling locations should include both the perimeter and interior of the field to obtain a representative estimate of weevil numbers throughout the field. See Proper Sweepnet Technique.

This monitoring procedure will also give an indication of the number of lygus bugs and diamondback moth larvae present and may serve as an early warning for those insects, provided that the same fields are monitored into the early pod stage.

Acknowledgements

The 2025 survey was completed by Agriculture and Irrigation, Plant and Bee Health Surveillance Section staff. Thank you to the Alberta Plant Health Lab survey technicians for your contribution to the survey.

Thanks to Jon Williams, Agriculture and Agri-Food Canada, Saskatoon, for preparing the map.

Historical survey maps

Resources

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