Black Vine Weevil

Black Vine Weevil is a pest of over 100 landscape plants. The adults feed on a wide variety of evergreen, deciduous, and herbaceous plants. The black vine weevil is also destructive in the larval form on yew , hemlock, rhododendron, and several other evergreens. It will sometimes feed on strawberry or impatiens.

Black vine weevil adults are black weevils with short, broad snouts. The weevils are approximately 6 mm (1/4 inch) long. The head is narrow, the thorax is medium and rounded, and the wing covers are broad and well rounded. The wing covers have fine yellow hairs and conspicuous corrugations which appear as lines down the back. Adults cannot fly; their wing covers are fused together.

All of the weevils are female; they reproduce parthenogenetically (by development of an unfertilized egg). Since the weevils do not fly, they disperse chiefly by walking, although they may be transported by man along with plants. The weevils feed at night and hide under leaf litter or in the soil during the day. When disturbed, the adults feign death. The larvae have a wrinkled c-shaped appearance. They are legless and white, with a well-developed brown head.

Black vine weevil larvae stunt or kill plants by feeding on the roots. Larger roots are stripped of their bark or girdled, or they have notches chewed out of them. The adult weevils chew the edges of the leaves, cut off the tips of needles or devour entire needles. Foliage is preferred to terminal growth.

Life Cycle: This pest overwinters as immature larvae in the soil. Mature larvae are 10-15 mm long and form resting (pupal) cells in the soil in early spring. Adults usually emerge from late May through June and in North America only females are known. They are active night feeders and when disturbed, adults drop quickly to the ground. During daylight hours adults hide in dark places on stems of plants with dense foliage or in leaf litter and mulch.

Adults require 21-28 days of foliage feeding prior to producing eggs. They may lay as many as 500 eggs over a period of 14-21 days. Eggs are laid in the soil near the base of host plants. They hatch in 10-14 days into small larvae that feed on roots until fall temperatures cause them to move deeper into the soil where they overwinter. Occasionally, a few adults may survive the winter inside homes.

Damage: Adults that feed along leaf margins produce typical crescent shaped notches. Careful searches should be made to try and locate specimens since several other weevils and some caterpillars can produce this same type of notching. Moderate to light notching seems to have little effect on plant health. The legless larvae prefer to feed on young tender roots of Taxus, rhododendrons and hemlock. If young roots become scarce or the soil becomes overly moist the larvae will move to large roots near the base of the plant. Large larval populations or moist soils cause feeding on the plant stem and the plant may be girdled.

particularly in northeastern counties where nurseries are located on sandy loam soils. This pest can also reach epidemic populations in polyhouses where liners and perennials are being grown. Occasionally, hundreds of field grown plants are killed with dramatic suddenness. Perennial producers occasionally open their polyhouses in the spring, only to find that many of the plants are dead because all their root systems have been eaten away.

Management: Manage adults by applying a registered insecticide according to label directions to host plant foliage during late May through June. Optimal timing of an application against the adult stage of this key pest may be achieved by doing the following. In early May place 6-inch by 6-inch boards on top of the mulch beneath several host plants. Pieces of burlap placed loosely around the base of a host plants may be substituted for the boards. During the middle of the day slowly turn over these boards or burlap. Note when you observe the first adult black vine weevil on the bottom of one of these monitoring surfaces.

Because adults need to feed on foliage for 21-28 days before they’re able to lay eggs, the first foliar application should be made three weeks after detection of the first adult. Since adults do not emerge at the same time, a second foliar spray should be applied according to label directions three weeks after the first one. Spraying foliage in early evening may increase control because adults become active on the host foliage a few hours after sunset.

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