Black Vine Weevils
BLACK VINE WEEVILS – CREATURES OF THE NIGHT
By Bailey Walten 1994 Newsletter
The Black Vine Weevil, Brachyrhinus salcatus, is a small 3/8 inch long snout beetle. Native to Europe it is named for its dark color and penchant for eating grapevines. Known to feed on at least 80 different species of plants, of primary concern is their frequent attacks on azaleas, rhododendrons, and yews as well as occasional infestations on camellias, laurels, cotoneaster, and euonymus.
It normally overwinters as an immature grub (larvae) that awakens from hibernation to resume feeding during April and May. This stage can be very destructive because grubs chew and bore into roots and can girdle plants by stripping bark from the base of stems along the soil line. As few as eight larvae can destroy enough roots to kill a large yew. If a yew turns yellow and then brown in spring and there is good soil drainage around the base of the plant, then it was likely caused by Black Vine Weevil. For this reason it has also been called the Taxus Weevil.
After feeding for a few months, these grubs will pupate in an earthen cell and emerge as adult weevils in June. You will probably never see them due to their nocturnal feeding habits. After hiding down in the soil all day, they crawl up the stems and chew on the foliage at night. The characteristic notching of the leaf margins is particularly obvious on infested azaleas and rhododendrons. High populations can result in the leaves being chewed down to where only midribs and large veins are left. It takes much closer examination to spot damage on yews. The notching tends to be concentrated on the portions of the plant closest to the ground.
After feeding for a little over a month, the adults mate and the females lay eggs underneath the plants in cracks and crevices in the soil or among plant litter around the hosts. These eggs hatch in ten days and the young grubs feed on fine root hairs, etc. until they go into hibernation.
Black Vine Weevils are difficult to control. They are easier to kill in adult stage by treating the foliage of the host plants with an insecticide (i.e. Turcam). We have seen an upsurge of Black Vine Weevils in the past few years and have found them hard to control with the basic ornamental program applications. Last season we began some spot treatments using Turcam (for licensed applicator use only) and obtained excellent results. More available products for their control would be insecticides like Merit and Scimatar.