2008 Cabbage Seedpod Weevil Forecast

Cabbage seedpod weevil was first found infesting canola in southern Alberta in 1995, since then, the weevil has spread to central Alberta and southwestern Saskatchewan.

The distribution and abundance of the cabbage seedpod weevil have been monitored yearly in western Canada since 1997. Predictive models based largely on climate data indicate that this pest will eventually disperse to all regions of canola production in western Canada, including the Peace River region.

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The 2007 survey indicated a large population of cabbage seedpod weevil in southern Alberta. While this is not a true forecast, experience has shown us that the numbers of weevils found at most sites south of Highway 1 have the potential to result in economically damaging populations in the next growing season. This high population may, however, be impacted by the hot summer we experienced in 2007. Experience has also shown us that high temperatures tend to reduce populations. The bottom line is that producers will need to check their 2008 canola crops as they come into flower. The earliest flowering canola crops tend to have the highest risk from cabbage seedpod weevil and should be monitored more closely.

Because the adult is the overwintering stage of the cabbage seedpod weevil, 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, although a severely cold winter with little snow cover could reduce the survival of overwintering adults. This map does not adjust for the emergence of the new generation in the fall.

The cabbage seedpod weevil takes roughly eight 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 bud-blasting (potentially reducing yield in dry years), larval feeding within developing pods (larva consumes about five seeds) premature shattering of damaged pods and new generation adults that emerge in the fall feeding on nearly developed seeds. The larval feeding alone can result in yield losses of 15 to 20 percent of each pod infested.

Because the adult is the overwintering stage of the cabbage seedpod weevil, 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, although a severely cold winter with little snow cover could reduce the survival of overwintering adults.

Cabbage seedpod weevil adult abundance can be monitored by taking sweep net samples. Sampling should begin when the crop first enters the bud stage and continue through the flowering period. Select ten locations within each field, and at each location count the number of weevils from ten 180 degree sweeps. Sampling locations should include both the perimeter and interior of the field to obtain an accurate estimate of weevil numbers throughout the field.

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

The 2007 cabbage seedpod weevil survey was carried out by Alberta Agriculture and Food with support from the Applied Research Associations and Agricore United (now Vitera).

2008 forecast based on 2007 survey data

Canola Council's Canola Insect Threshold Update Summer 2008

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2008 Cabbage Seedpod Weevil Forecast

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