Integrated Pest Management Guide

BLACK VINE WEEVIL, Otiorhynchus sulcatus (F.)

Pest Status: This is the most common weevil pest in cranberry beds. In British Columbia, weevil damage is usually restricted to beds that are not flooded at harvest.

Life cycle and feeding habits: The adult black vine weevil is a black snout beetle about 8 - 9 mm (1/3 inch) long. Adults emerge from pupal cells in the soil from mid-June to the end of June; some adults may live through the winter. Adults feed on foliage for 4 - 6 weeks before egg-laying begins. Black vine weevils are all flightless females so there is no mating before egg-laying. Eggs are laid at the soil surface during the summer beginning in July and hatch within 2- 3 weeks. The newly emerged larvae descend to feed on rootlets and, later, on the larger roots and root bark. The larvae are white, legless, have a brown heads, and often curl their bodies into the shape of the letter C. They feed from the time they emerge from the egg until pupation the next spring. They may be inactive during very cold spells in winter. There is only one generation per year.

Monitoring: In spring and in fall, the larval population of black vine weevils can be monitored by rolling back damaged vines and looking through the top 5 cm (2 inches) of soil for girdled vines and weevil larvae curled in a "C". Mature black vine weevil larvae are about 8 - 9 mm (1/3 inch) long in spring. In fall, they are younger, smaller and harder to see.

Weevil larvae can completely girdle roots up to the crown of the plants. Damaged vines look similar to girdler-damaged vines, but lack the frass left by girdler larvae at feeding sites. Symptoms of damage (wilting, weakening, browning, death) begin to appear in May or June and intensify through the season.

Monitoring for weevil adults is done using a sweep net. On warm, still nights after dusk in early July, sweep beds once or twice a week until eggs begin to mature within the adult weevil and egg-laying begins. To determine the presence and maturity of eggs within an adult weevil, pinch the abdomen of about 10 weevils and look for spherical white eggs. When ready to lay eggs, the weevil's entire abdomen contains eggs and little else. If weevils are found, treatment is recommended. Weevil detection can also be done by observing vegetation in the vicinity of the cranberry bed. If present, characteristic leaf-notching caused by feeding adults will be readily seen on plants such as salal near the cranberry bed. Notching on cranberry can be difficult to see.

Control: When flood water is used during harvest, most weevil larvae will be drowned. On dry-pick farms or young, unharvested beds, weevil larvae and pupae can be drowned by flooding beds in winter.

Hold water on the bed for 2 - 4 weeks, if the plants can safely sustain water for that long. Re-infestation can occur by recycling flood water from one bed to another. There are no insecticides registered for control of adult black vine weevils.

Nematodes can be applied in spring (May) and in fall (September) to target black vine weevil larvae in the soil. Soil temperatures should be at least 13º C (55º F) and lots of irrigation applied to the bed before and after nematode application.
 

Black vine weevil adult	Black vine weevil larva

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