Cabbage Seedpod Weevil

Cabbage seedpod weevil has been seen in canola fields throughout southern Alberta and southwestern Saskatchewan as crops have started to bolt, with some fields in early flower. The proper way to sample for cabbage seedpod weevil adults is with a sweep net. Begin sampling when the crop first enters the bud stage and continue through the flowering period. For more information on determining the appropriate growth stage, refer to the following section of the Canola Growers Manual: http://www.canola-council.org/chapter3.aspx#ch3_sec3 .

Select 10 locations within each field and at each location, count the number of weevils from ten 180° sweeps. Sample both the perimeter and interior of the field to obtain an accurate estimate of weevil numbers throughout the field. For more detailed information on proper sampling techniques, refer to the following link: http://www.canola-council.org/canola_resources/product10.aspx .

The economic threshold for the weevil is 20 to 30 in 10 sweeps, depending on crop price.

Research has shown that weevil migration into canola begins at the bud stage and peaks at early to mid-flowering. It is important not to spray too soon, as the weevil will typically continue to invade for at least a week to 10 days after the first flowers open. The optimum time to spray for cabbage seedpod weevil is early flowering (10% flower if possible). Spraying at 10% flower will allow the weevils more time to move into the field, while at the same time it is still early enough to keep them from laying any significant number of eggs in the newly forming pods. Spraying after 10% flower when populations are at or above threshold may not only result in yield loss, but will also impact beneficial insects including pollinators who have moved into the field. It is important to keep in mind canola’s ability to compensate for weevil feeding on buds and stems where moisture is not limiting. Where moisture constraints are present, the ability to compensate may be reduced, and using the lower end of the threshold range may be appropriate.

For more information on the cabbage seedpod weevil, refer to the cabbage seedpod weevil section at the following link: http://www.canola-council.org/contents10b.aspx