White pine weevil adult.
White pine weevil weevils will eventually kill the tops of trees.
White pine weevil damage to Colorado spruce.
Species: Pissodes strobi (Peck)
Distribution: Most of northern North America
Prefers eastern white pine and spruces, occasionally attacks other pines and rarely Douglas-fir. In the Western States, this pest is known as the Englemann spruce weevil and Sitka spruce weevil.
The larvae do the most obvious damage when they kill the tree leaders. Leaders with expanding buds droop, forming the typical "shepherd's crook." The larvae may travel past the first whorl of branches resulting in their death. The adults feed on branches and shoots causing considerable sap flowing. However, this generally does not kill branches.
Description and Life Cycle:
The weevils are often hard to see, but their damage, die back of the leader, is easy to spot. The adult weevils are light reddish-brown with several patches of white on the wing covers. Like most weevils, the adults have a long snout-like beak from which arise elbowed antennae. The larvae are found under the bark of the dying leader, and are white, legless, C-shaped grubs with brown heads.
This pest overwinters in the adult stage hiding in the duff under trees. In early spring, usually early to mid-April, the adult females climb to the leaders of trees and feed through small holes chewed in the bark. This feeding causes sap to run down the leader. Eventually, the females will insert eggs into these feeding wounds. The larvae hatch in about a week and feed just below the bark. The larvae continue to feed downward, girdling and killing the shoot as they go. The larvae mature and pupate in mid-July. The pupae rest in cells carved into the central wood and lined with sawdust. The adults emerge in late July and early August. The new adults feed on the upper tree branches, making small puncture wounds. As winter approaches the adults return to the duff to hibernate.
All controls are intended to kill the adults or larvae before the tree leaders are damaged.
Option 1: Cultural Control - Prune Infested Leaders - As soon as infested leaders droop, cut the leader out just below where the bark discoloration stops. Do not throw this pruned leader on the ground as some of the weevils may survive. If the damage is stopped before the first whorl of branches is reached, a new leader can be easily trained. Damage below the first whorl may mean that the tree can not be harvested except for foliage usage.
Option 2: Cultural Control - Remove Weevil Breeding Areas - Try to destroy or remove eastern white pine in nearby forest stands. These trees serve as sources of infestation.
Option 3: Chemical Control - Late Summer and Fall Insecticide Sprays - If a heavy infestation is detected, sprays in mid-August through September can greatly reduce the adult weevil population. However, inspection of leaders in the spring should be done to determine success of the fall application.
Option 4: Chemical Control - Spring Insecticide Sprays - Early spring sprays for adult control is the most commonly used technique. Look for the sap flow coming from leaders in early spring. This indicates that the adults are feeding and sprays should be applied immediately. Systemic insecticides are more effective because they kill any larvae already inside the leader. Adult activity usually begins whenever daytime temperatures are 70°F or more.