Cabbage Seedpod Weevil-FAQ
Description of cabbage seedpod weevil (Ceutorhynchus obstrictus)
The adult cabbage seedpod weevil is a small, ash-grey beetle, three to four mm (1/6 in.) long. Characteristically, it is a hard-bodied insect with mouthparts that include a long snout. The larvae are white, grub-like organisms that feed within the seedpod of the host plants.
What damage does cabbage seedpod weevil cause?
Plants commonly attacked by the weevil include members of the Brassicaceae or mustard family, including cultivated crops and weed species. Flower buds and pods are the main parts vulnerable to damage. Because the damage is concentrated on these sections, the damage is substantially higher compared to the damage caused by insects to leaves and other vegetative parts.
What is the lifecycle of the cabbage seedpod weevil?
There is one generation per year. The adults over-winter in Saskatchewan and emerge in the spring migrating from weeds into host crops. They feed and mate, with the females laying eggs onto developing pods. After hatching, the larvae feed within the developing pod - consuming seeds. When mature, the larvae exit through the pod wall, dropping to the ground to pupate. Later, the emerging adults will feed on the plants causing additional damage. It takes the weevil close to eight weeks to complete development from egg hatch to adult.
Which areas of the province is cabbage seedpod weevil a threat?
The cabbage seedpod weevil moved into southwestern Saskatchewan from Alberta. The weevil expanded its range to west-central and south-central areas of the province but a low populations. Higher populations which require insecticide application have still been largely restricted to southwestern Saskatchewan.
How should I monitor my fields for cabbage seedpod weevil?
Sweep nets are required to help monitor fields for Cabbage Seedpod Weevil. Monitoring should begin at the early bud stage up through the flowering stage. Sweep perimeter areas, as well as interior sites using 180° sweeping motions. Choose 10 sites within each field and estimate the average number of weevils. Often, infestations will be more concentrated in field margins early in the season. Control measures may only be needed in the concentrated areas. For information on how to use sweep nets see Sakatchewan Agriculture's Economic Thresholds of Insect Pests at www.agriculture.gov.sk.ca under Production/Crops-Insects.
How do I control cabbage seedpod weevil?
Cultural control methods include interception strategies (using specific crops to trap insects before the protected crop generates buds). Planting non-host crops (e.g. cereals, pulses) or resistant crops such as yellow mustard (Sinapis alba) will help to avoid damage from this insect.
There are registered insecticides available to control this insect in crops. See the Saskatchewan Agriculture's Guide to Crop Protection for more information.
Chemical control is recommended when an average of three to four weevils are collected per sweep following the monitoring guidelines above. When the value of canola exceeds $8 per bushel, an economic threshold of two adult wevils per sweep is more applicable. The best time to spray is when the crop is in the 10 to 20 per cent flowering stage. Spraying should be done later in the day to minimize impact on beneficial insects (parasites) that help to control cabbage seedpod weevil populations.
Are there any natural biological controls that affect the cabbage seedpod weevil?
Two species of wasps have been found on the Prairies: Microctonus melanopus is a wasp that parasitizes adult weevils, and Trichomalis perfectus, is a wasp that attacks weevil larvae within the pods. They are a very important biological control organisms that affect Cabbage Seedpod Weevil populations.
Alberta Agriculture and Rural Development
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Guide to Crop Protection provides information on the use of herbicides, fungicides and insecticides for control of weeds, plant diseases and insects.
Host plants of the cabbage seedpod weevil all belong to the mustard family, and include canola, brown mustard, cole crops and cruciferous weeds.