Insecticides for variable staged crops

June 26, 2015 - Issue 15

Cabbage seedpod weevils can arrive early, but this is still too early to spray.

Cabbage seedpod weevils can arrive early, but this is still too early to spray.

Cabbage seedpod weevils are one example of an insect where crop stage is a factor in the management decision. Weevils lay their eggs in developing pods, and these larvae feed on canola seeds inside the pods. The rule of thumb is pods less than 3/4” are too small for egg laying. If some plants are forming pods and the rest are still bolting, waiting will improve overall spray timing and return on investment.

Weevils are attracted to the flowers, so spraying before general flowering will miss the weevils that migrate into the crop at that stage.

The time to assess the field is at 15-20% flowering. Spraying cabbage seedpod weevil (CSPW) when canola is at the bud stage provides no economic benefit. Base the spray decision on sweep net counts. The economic threshold is 20 CSPW per 10 sweeps generally across the field.

Further reading:

Assess the real cause of bud loss in pre-bolting canola

Canola Watch