Description of the Pest
The adult cribrate weevil is dark brown to almost black. It is about 0.33 inch (8 mm) long and has longitudinal striations on its back. Adult emergence often begins in late May and adults are present all summer. They are nocturnal and flightless - hiding in cracks in the soil, under clods, or between fruit during the day. At night, they emerge and crawl up the trunk to feed on foliage.
Young trees may be stunted or killed by defoliation and bark feeding. Damage on mature trees is most serious when a large population feeding on the petiole results in premature fruit drop, water stress, and subsequent smaller fruit size and yield. Notching out of the edge of the leaf is characteristic of initial foliar feeding giving the leaf a ragged appearance. With higher populations, the whole leaf except the veins, as well as the bark on twigs and pedicels may be consumed. Young trees are particularly susceptible to defoliation, stunting, and tree loss. The white larvae overwinter on the roots but have not been associated with significant damage to apple trees.
Cribrate weevil is an occasional pest of apple trees in the Central Coast and foothill regions. No currently registered insecticide treatments have been shown to be effective against this pest. Preplant fumigation may reduce potential problems, but for existing trees the primary control is application of sticky material to the trunk. A three- to four-inch band of sticky material such as Tanglefoot will prevent adult weevils from climbing the trunk. The sticky material needs to be re-applied when it becomes dirty. While applications of these sticky substances have not appeared to cause phytotoxicity, thin bark will slough off, and it may be safer to apply these materials over tape or painted areas.