Hylobius pales (Herbst)
Symptoms and Damage
The pales weevil, Hylobius pales (Herbst), is a serious pest of coniferous seedlings that can cause considerable twig and tree mortality. Adults feed on tender bark of twigs and bases of seedlings. The bark is chewed off in irregular patches and the girdling causes twig and tree mortality. Trees two to five years old are severely damaged and killed, but one year old seedlings are avoided. White pine is the preferred host, although severe damage to all Maine conifers may occur on trees up to 1/2 inch in diameter. The greatest damage is inflicted in the fall from September to mid-October in the vicinity of adult emergence from stumps and slash. This insect pest is a recurrent problem in Christmas tree plantations where periodic harvests leave many pine stumps suitable for weevil breeding.
The beetles feed on the bark of all native and planted conifers. White pine is the preferred host.
Description and Habits
The adults, robust, dark reddish-brown to black snout beetles from 1/4 to 3/8 inch (6-10 mm) long, overwinter in the soil at the base of seedlings. During April and May the adult weevils emerge from hibernation and feed at night on the tender bark of young trees. The weevils return to the soil to hide during the day so that infestations are not noticed until twigs and seedlings begin to wither and die. Adult weevils feed until they are ready to lay eggs in July. Eggs are laid singly in freshly cut pine stumps and slash. The adults are attracted to areas by the odor from freshly cut pine stumps and slash and can migrate up to several miles to new breeding grounds. Fresh pine burns also provide ideal breeding material. The eggs hatch in about two weeks and the grubs or larvae feed under the bark until they mature in late August and early September. Pupation then takes place in a shallow cell in sapwood, and requires about 2 weeks before the adults emerge in September.
Damage to young trees can be avoided by delaying planting operations in the area until the third season after logging, thinning or after a burn in coniferous stands.
If the planting of conifers is attempted in the fall of the first season, or in the spring of the second season after the logging operation then chemical controls are recommended to reduce the damage. Natural reproduction can be protected by spraying stumps and slash to reduce pales weevil populations: a) apply chemical in late June to kill the weevils before they lay their eggs in freshly cut stumps or large slash; or b) spray in April to kill the weevils as they emerge from the breeding material. Planted seedlings should be sprayed in late August of the first fall, or/and again in April of the second season after cutting to protect them against feeding by the adult weevils. Carbofuran** and chlorpyrifos are both registered for control of the pales weevil.
*NOTE: These recommendations are not a substitute for pesticide labeling. Read the label before applying any pesticide. Pesticide recommendations are contingent on continued EPA and Maine Board of Pesticides Control registration and are subject to change.
Caution: For your own protection and that of the environment, apply the pesticide only in strict accordance with label directions and precautions.
MAINE DEPARTMENT OF AGRICULTURE, CONSERVATION AND FORESTRY
Maine Forest Service - Forest Health and Monitoring Division