Canola School: Sweep well ahead of deciding to spray for cabbage seed pod weevil

Cabbage Seedpod Weevil | Photo Courtesy of Alberta Agriculture and Foresty

By early July, many canola fields across the Prairies are in the beginning stages of bolting. According to Héctor Cárcamo, research scientist with Agriculture and Agri-Food Canada at Lethbridge, Alta., that’s a great time to start thinking about the cabbage seed pod weevil.

Before worrying about thresholds and spray timing for the insect pest that can be quite detrimental to the final yield, it’s important to dust off the ol’ trusty sweep net, and see what is actually out there.

“Make sure you get inside the field because if you only sweep the edges of the field, you’re going to get a very inflated count,” explains Cárcamo. “For example, if you just sweep the field in one spot, and you find say four weevils per sweep; the threshold is around three to four weevils. Now, if you move 50 meters into the field, you will find only half as many weevils.”

The extra time to get a complete picture of the insect pressure in the field is a small price to pay, compared to the thousands of dollars you might spend spraying fields unnecessarily.
Check out the full conversation between Carcamo and RealAgriculture’s Kara Oosterhuis, below:

Bolting may be the time to begin scouting for the cabbage seed pod weevil, however, it’s not necessarily time to decide whether you are spraying or not. Cárcamo recommends waiting until you see the first flower — and then waiting about a week. If the temperature is average for that week, your crop will end up being at 20 per cent flowering — and that’s the time to start thinking about control, if warranted.

“Before that time there is a bit of a risk that you may spray too early, and then there could be another wave of insects coming into your field. If you spray too late, then there’s a potential that the weevils would have already laid the eggs, because they lay the eggs on small pods that are about one inch long,” he explains. “So you really have to think about the timing correctly.”

Some of the research that has been conducted over the years has shown that you can lose two to three bushels per acre, so keeping an eye out for the insect can certainly be worth your time.