The most severe damage is caused by the grubs (larval stage) which feed on the feeder roots and cortex of larger ones, and may girdle the root crown. The above-ground symptoms are of general plant unthriftiness including stunting and yellowing or off-color foliage. Root feeding often results in death of the plant and it is at this late stage of injury that home gardeners often notice the problem. Plants may fail to put out new growth in the spring as a result of the root injury, or may put out the first flush of new growth, and subsequently die. Adult weevils feed on foliage, chewing out characteristic notches, and while foliar damage is often not serious, it can be unsightly. Adults are occasionally found indoors during the winter months. A few do overwinter and seek shelter near foundations and occasionally wander inside. They are a nuisance to find, but a threat only to actively growing plants in the house. Removing by hand when seen is the best control for a few individuals inside the home.

DESCRIPTION

The adult is a black wingless weevil (snout beetle) about 3/8 inch (10 mm) long. All of the weevils are females and they reproduce parthenogenetically. Since the weevils do not fly, they disperse chiefly by walking, although they may be transported by man with infested plant material. The grub is a legless, white (with a brown head) larva with a wrinkled c-shaped appearance and is found in the soil under host plants.

LIFE HISTORY

There is one generation of the black vine weevil each year. Adults usually emerge between mid-May and late July and live for several months. Adults may overwinter and be found in early spring. The weevils feed at night and hide under leaf litter or in the soil during the day. When disturbed, the adults feign death. After 3-4 weeks of feeding the females begin to deposit eggs. Eggs are dropped indiscriminately to the ground under the plants (as many as 500 per female!) over their entire life. If houseplants are placed under shrubs during the summer, eggs may be deposited on the soil of the containers. Ten to 14 days later the grubs hatch and burrow down into the soil searching out roots to feed on.

Larval feeding occurs through the growing season but when colder temperatures arrive, grubs burrow deeper in the ground to overwinter. They resume feeding the following spring for a short while before they enter the pupal stage. Pupation lasts about 1 month and adults are most abundant from early June to mid-July.

MANAGEMENT

Look for symptoms (monitor plantings) of feeding injury by adults, and/or use a flashlight at night (adults are nocturnal) during early to mid-June to inspect plants for the presence of weevils. Injury will be easy to see on broad leaved evergreens such as rhododendron, but may be hard to find on Taxus. Weevils may be feeding on leaf edges, especially near the trunk. Pit fall traps or beating sheets are sometimes used to monitor adult activity. Where possible, quarantine plants with leaf notches.

Treat for the adults before egg laying can occur (2 to 3 weeks after emergence). The insecticide acephate (Orthene) is recommended for the control of black vine weevil adults on Taxus, Rhododendron and other ornamental plants. Two applications should be made, one 3 weeks after adults are first seen (or in mid-June) and a second 3 weeks later. Insecticide applications should be made late in the day (weevils are nocturnal feeders). Be sure to follow the label directions when using any pesticide.

If houseplant roots are found to be infested with larvae, discarding the plant may be the best practice. One might try washing off the roots and repotting, but success will depend on the amount of damage already done (often too late by the time one notices it).