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White Mould and Cabbage Seedpod Weevil Mangement in Canola

Flowering has begun in many winter canola fields. Two key pests in winter canola at this growth stage are cabbage seedpod weevil (CSW) and white mould (a.k.a. Sclerotinia stem rot). These are also both pests of spring canola, and the management recommendations are the same for both types of canola.

Cabbage Seedpod Weevil

When to scout: CSW may begin to appear just prior to bolting and are found on flower buds until pods begin to form. Monitor from the first appearance of flower buds through to the end of flowering. They emerge from overwintering sites when temperatures are above 15°C.

What to look for: Adults are a conspicuous, dark grey weevil with a prominent curved snout and measure 3-4 mm in length (Figure 1). If present, they are usually easily observed on flower buds and are most abundant at field edges.

Adult weevils will feed on flower buds causing bud abortion, but the adult feeding damage rarely causes economic yield losses (Figure 2). Where there is adequate moisture, the canola plant can compensate for some loss of buds. Yield reduction is caused by the CSW larvae, which feed on seeds within developing pods and create exit holes leading to shatter losses (Figure 3).

How to scout: Scout fields using a sweep net; conduct 10 sweeps (180˚ from shoulder to shoulder) across the top of the plants in ten different locations within the field and count the number of weevils. Sweeps should be conducted in the interior of the field as well as the perimeter. Contact Meghan.Moran@ontario.ca for information or assistance with scouting.

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