The black vine weevil, also known as the taxus weevil, has become a serious pest in nurseries across the northern United States since its introduction from Europe approximately 150 years ago. It has a wide range of host plants including: Taxus (yew), rhododendron, hemlock, azalea, euonymus, cyclamen, laurel, gardenia, juniper, impatiens, boxwood, holly, grape, strawberry and various other woody and herbaceous plants.
Black vine weevils have one generation per year (more if in a greenhouse). The adult weevils are all flightless female beetles that disperse only by crawling. Males are not known to occur, and females produce eggs without mating. The 5/8-inch weevils are black with light yellowish or gray spotting or checkering on their backs.
The adults feed at night on the foliage of host plants causing crescent- or notch-shaped injuries along the margins of leaves and needles. The notching of the leaves is much less serious than the injury caused by the grubs (larvae) feeding on the roots. Adults hide during the day in leaf litter, other debris or soil under the plants.
Black vine weevils overwinter in the soil as larvae or as adults in plant debris, buildings or other sheltered areas.
The adults tend to be more abundant after wet summers and are commonly found in and around houses, being attracted to lights. They do not cause a household problem indoors other than their presence.
Eggs are laid in the soil at the base of host plants and hatch into larvae in about 10 days. The larvae are legless, slightly C-shaped white grubs with brown heads. Larvae feed on the roots of host plants and in heavy infestations may destroy most of the small feederroots. Larger roots and the crown may be girdled (removal of the bark in a ring) resulting in wilting, yellowing of the foliage, and possible death of the plant.
Plants should be examined very carefully
before purchase to detect notching of the leaves. Plants showing
signs of adult feeding should not be purchased be
cause larvae may
be in the soil of the root ball. Many infestations of black vine
weevil are the result of purchasing infested plants. If controls
are needed, they are best directed at the adults to kill them
before they lay eggs. Larvae are usually found deep in the root
ball, and cannot be reached well with an insecticide to provide
good control.
Research by Dr. James Hanula, Connecticut Agricultural Experiment Station, New Haven, has determined that adults emerge from the soil from late May to early June but do not begin to lay eggs until three to four weeks after emergence. Therefore, any insecticide treatments do not have to be applied until mid- to late-June.
Susan Mulgrew, University of Massachusetts, Amherst, has developed a method of monitoring black vine weevil adults using burlap traps. A piece of burlap (approximately four feet by three feet) is bunched lengthwise to create folds and then is wrapped around the base of a host plant. The adult weevil will crawl into the folds of the cloth to hide during the day. The traps can be inspected by gently removing the burlap and examining it for weevils.
If black vine weevil adults or fresh feedings are found, an insecticide should be applied thoroughly to the plant and a surrounding two foot radius of soil within three to four weeks after first detection. If weevils are found only in certain areas of a field or nursery, growers should consider applying spot treatments. This would consist of spraying only the infected areas and a narrow buffer zone of uninfested plants. Burlap traps placed both inside and outside the sprayed areas can be used to help determine if the treatment provided adequate control. Because the insecticide residues are short lasting, repeat treatments will usually be needed at three-week intervals until no more black vine weevil adults or fresh leaf notchings are found.
Further research by Dr. Hanula, however, has found that a single application of fenvalerate (Evercide*) applied two weeks after detection of the first adults provided good control throughout the season. Other insecticides labelled for black vine weevil control include:acephate (Orthene), bendiocarb (Turcam*, Dycarb*) and fluvalinate (Mavrik). Use these according to label directions. NOTE: None of these are registered for use on food crops.
*Restricted to professional or commercial pesticide applicator use only.
Prepared by: Richard
Packauskas. Entomologist, and
Roger G. Adams, Integrated Pest Management Program Leader.
June 1990.
Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.
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