Willow (Salix)-Poplar-and-willow borer

Cryptorhyncus lapathi

Pest description and damage The adult poplar-and-willow borer is a black and pink to cream-colored weevil (a flightless snout beetle) about 0.375 inch long. The larvae are white, legless, and about 0.25 inch long at maturity. Larvae feed by mining beneath the bark of trunk and branches. In late summer, feeding larvae expel large quantities of sawdust-like frass (excrement) through holes in the bark accompanied by flow of a thin sap. Larval feeding may girdle branches, resulting in breakage, leaf wilt or eventual branch death. Severe infestations cause lumpy, swollen bark, with cracks and bark scars with exposed wood. Old wood may produce large numbers of new shoots. Willows are the preferred host, but the poplar-and-willow borer also attacks poplars. The adults chew small holes in the bark of twigs and shoots, introducing a fungus which may cause shoots to wilt. This insect has become a serious problem in hybrid poplar plantations, and in willows grown for the cut flower industry and restoration plantings. In landscapes, damage is most common on native willows.

Biology and life history The adult weevils lay eggs just under the bark in the cambium, mostly near lenticel, buds and wounds in late summer and early fall. Eggs hatch soon after they are laid and begin to feed under the bark, creating a small chamber in which they hibernate over winter. They resume feeding in the cambium, then bore into the heartwood to pupate and adults emerge in late summer. It only takes one year from egg to adult but the adults can live up to three years so that the weevils are increasing over time. This allows an accelerated buildup of this insect.

Pest Monitoring Adults may be dislodged from branches by beating foliage. In spring, evidence of infestation is a sap flow down the trunk of the tree and moist sawdust being pushed out of the gallery. Adults are commonly found walking on the trunk or branches, especially at night. Look also for wilting of suckers and pronounced holes in the young stems from adults feeding.

Management-cultural control

Hand-pick adults when noticed on trunk and branches. Beating may also dislodge more than are visible. Remove infested branches showing evidence of attach and dispose of the prunings in a chipper or yard waste. Don't allow wood to remain for weevils to emerge.

Management-biological control

Little is known of the effectiveness of biological control.

Management-chemical control

See: