2010 Cabbage Seedpod Weevil Forecast

Cabbage seedpod weevil was first found infesting canola in southern Alberta in 1995, since then, the weevil has spread to south-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 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 2009 survey covered all the canola growing areas of Alberta but the cabbage seedpod weevil is still only found in the southern areas. There was no significant expansion of the cabbage seedpod weevil range in Alberta in the past year. Of particular note is the low numbers of weevils found in Kneehill and Mountainview counties. Both of these counties have had weevils for several years but the numbers have still not developed into damaging levels. The weevil has still not been found in Starland county. In eastern Alberta the northern range is in Special Area #4 around Consort and once again the cabbage seedpod weevil has been in this area for several years but has not pushed further north. Wheatland county has shown a dramatic increase in 2009 and producers in that area need to be aware of the need to scout their fields in 2010.

As of 2009 the cabbage seedpod weevil is not found in central Alberta or in the Peace River region. The 2009 survey indicated a higher population of the weevil in southern Alberta than in 2008. Many producers were required to take management action to prevent crop damage and losses. 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 population may further increase in 2010 due to favorable conditions for larval and pupae stages in the late summer of 2009. Experience has shown us that cooler temperatures and rainfall in August favors the development of the new generation of weevils. Any producers that grow canola in southern Alberta and into the south end of central Alberta will to check their 2010 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 very closely.

The adult is the overwintering stage of the cabbage seedpod weevil and because of that 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.

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 per cent of each pod infested and is the most important damage from an economic perspective.

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 is best monitored by using 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 a representative 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 2009 cabbage seedpod weevil survey was carried out by Alberta Agriculture and Rural Development with support from the Applied Research Associations (SARA, CARA, BRRG, GRO, LARA, and SARDA) and Agriculture and Agri-Food Canada.

For more information on cabbage seedpod weevils and their management contact the Ag-Info Centre at 310-FARM (3276).

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2010 Cabbage Seedpod Weevil Forecast

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