The white pine weevil, Pissodes strobi (Peck), is most common in Ohio in the northern and eastern counties. Its range in eastern North America is generally where eastern white pine grows naturally. It is also common in the northern Rocky Mountains to the West Coast where it is called the Sitka spruce weevil.
White pine weevils prefer eastern white pine and various spruces. They will occasionally attack other pines and rarely Douglas-fir.
The larvae do the most damage by killing leaders of infested trees. Leaders with expanding buds droop, forming the typical "Shepard's hook." 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 the branches.
The weevils are often hard to find 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 knobbed antennae. The larvae, which are found under the bark of the dying leader, are white, legless, C-shaped and have brown heads.
This pest overwinters in the adult stage hiding in the duff under trees. In early spring, 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 sap wood and lined with straw like sawdust. The adults emerge in late July and early August. The adults feed on the upper tree branches, making small puncture wounds. As winter approaches, the adults return to the duff to hibernate.
All controls should be targeted to kill the adults or larvae before the tree leaders are damaged.
Strategy 1: Mechanical 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.
Strategy 2: Remove Weevil Breeding Habitat - In Christmas tree plantations and ornamental nurseries, try to destroy or remove eastern white pine in nearby forest stands. These trees serve as sources of infestation.
Strategy 3: Spring Insecticide Sprays - This is the most commonly used technique. Look for the sap flow coming from leaders in early to mid-April. This indicates that the adults are feeding and sprays should be applied immediately. Systemic insecticides are often more effective because they kill any larvae which may already be inside the leader. See Bulletin 504 for a current listing of insecticides registered for this purpose.
NOTE: Disclaimer - This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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