Canola School: Sweeping and scouting for cabbage seedpod weevil


Cabbage seedpod weevil can cause considerable yield loss to a canola and other brassica crops, such as mustard. As adults, the pest is three to four millimetres in length, is ash-grey in colour, and has a prominent curved snout, similar to other weevils.

Meghan Vankosky, field crop entomologist at Agriculture and Agri-Food Canada Saskatoon, joins Kara Oosterhuis for this Canola School episode to talk scouting for cabbage seedpod weevils, the damage they can do, and when to take action.

“The best way to look for cabbage seedpod weevil is actually to sweep for them,” says Vankosky. “You’re going to find them in the upper canopy of the plant, because at this time of year as the flowers are starting and the buds are coming out, the weevils are going to be laying eggs into the flowers and into the pods.”

Sweep at the level of foliage and flowers, when plants are at the 10 to 20 per cent flowering range, then check the net to see how many cabbage seedpod weevil there are. The pest will be more active when the temperature gets into the 15 to 20 degrees C range, and scouting into the afternoon is also a good idea, says Vankosky. Adults emerge as the crop is starting to bolt, and as it’s starting to flower, then a bit later will lay eggs.

“Adults will feed on the foliage, so you’ll find maybe some chewing damage on the leaves lower down in the canopy,” says Vankosky. “But, the real damage to yield comes from the larvae — they’re actually going to feed inside the pods.”

Larvae will feed on developing seeds inside the pod, then will chew a hole through the pod to exit, which can weaken the pod, resulting in shatter at harvest, and even more yield loss. (Story continues below video)

Vankosky says the threshold is three to four weevils per sweep, but to take 10 sweeps in at least four to five locations. If there are more than three to four weevils per sweep, consider taking action.

As of yet, there aren’t any direct parasitoids or beneficial insects go after cabbage seedpod weevil, but Vankosky says that it’s still important to protect the beneficials out there, because they could be eating other pest insects.

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