How to Manage Pests

Pests in Gardens and Landscapes

Black vine weevil—Otiorhynchus sulcatus

The black vine weevil feeds on many garden and landscape plants such as azalea, rhododendron, euonymus, grapes, and liquidambar. Adult weevils are roughened, hard-shelled flightless beetles, approximately 0.5 inch long, black in color with small patches of white scales on the forewings. They have elbowed and clubbed antennae and their head is elongated into a long, broad snout.  Adults do not fly. Larvae are whitish grubs.

Identification of species | Life cycle

Damage

Adults generally feed on foliage. Leaves or flowers appear notched or ragged, and leaves or needles may be clipped from twigs. Where budbreak coincides with adult emergence, a high percentage of primary buds and new shoots may be destroyed. Otherwise damage is not serious. The most serious damage is done by larvae, which feed on roots and can kill or weaken some plants, especially azalea and rhododendron, increasing damage from root diseases such as Phytophthora. Feeding on branches can cause limb breakage. Feeding galleries may be seen in the crotches of limbs

Solutions

Handpick and destroy adults to prevent more serious damage. For rhododendrons, plant less susceptible species. Provide cultural care to keep plants vigorous and better able to tolerate damage. Check roots before planting to make sure they are free from larvae. Trim branches that provide a bridge to other plants or the ground and apply a 6-inch band of sticky material to trunks to prevent flightless beetles from feeding on foliage. Trapping may help. Parasitic nematodes may also be effective in controlling larvae. Foliar sprays are not generally necessary and should be avoided as they are likely to disrupt the biological control of other pests.  However, if treatment is warranted in woody ornamental plantings, timed insecticides applied to leaves can control adults.

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Adult black vine weevil on euonymus leaf

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Characteristic weevil damage


Statewide IPM Program, Agriculture and Natural Resources, University of California
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