White Pine Weevil Damage is Becoming Evident

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White pine weevil (Pissodes strobi) larval feeding damage is now becoming very evident in southern Ohio.  This means that localized weevil populations may be reduced by removing and destroying infested conifer terminals.  Overwintered females deposit eggs in early spring in the terminals of a wide range of conifers including Douglas-fir, all spruces, as well as Scotch, jack, red, pitch, and eastern white pines.  After the eggs hatch, the resulting white, legless, slightly curved, grub-like larvae tunnel downward just beneath the bark feeding on phloem tissue until pupation.  The tops of weevil infested trees become wilted, turn brown, and die.  Main leaders are often curved into a "shepherd's crook."

White Pine Infested with White Pine Weevil

Removing the paper-thin bark from infested leaders will reveal reddish-brown frass (insect excrement) and weevil larvae.  As the larvae near pupation, they form so-called "chip cocoons" by excavating tub-shaped chambers in the xylem and surrounding themselves in Excelsior-like wood fibers.  New adults emerge through the bark creating small, round exit holes.  The adults mate and feed on bud and twig tissue; however, their damage is inconsequential.  The weevils then move to the duff beneath conifers to spend the winter.

Spruce Infested with White Pine Weevil

There is one generation per year and populations may be reduced by removing the infested terminals before adult weevils emerge.  Wilted terminals should be pruned from trees and the cut ends closely examined to determine if the cut top contains all of the weevil larvae.  Larval tunnels appear as round to oblong holes in the phloem ring that are filled with reddish-brown frass.  If larval tunnels are found in the portion of the terminal that remains on the tree, another cut should be made further down on the stem.  Infested material must be destroyed since the weevils will complete their development in cut tops left on the ground.  Young conifers typically respond well to training a lateral branch to become a new terminal.

Weevil Larva in Pine Phloem

 

Infest Cut Leader w-Weevil Tunnels

 

Infested Leader Cut Below Larval Activity

 

Years of successive weevil damage to terminal leaders will eventually create "cabbage trees" which are short, squat trees with multiple terminal leaders.  The weevil is common to the northeast part of the state and it is becoming common to central Ohio; however, it remains less common in the southern part of the state.  Consequently, the weevil damage may be misdiagnosed as being caused by other problems such as root injury or drought stress, or symptoms may go unnoticed allowing localized populations to expand.