White Pine Weevil
The white pine weevil, Pissodes strove, is a native North American insect that earned its name when found causing injury to the eastern white pine. In the Western States, it is also known as the spruce weevil because of its almost exclusive attacks on spruce trees rather than pine trees.
Identifications:
The adult insect is a 1/4 inch long weevil that is mottled brown in color. This coloration acts as camouflage and makes the insect hard to detect on trees. Characteristic of all weevils, the mouthparts are prolonged into a snout that bears a pair of chewing mandibles or theeth at the tip. Larvae are small and cream colored legless grubs with a reddish-brown head. Larvae are only visible by scraping away the outer bark of infested terminal shoots.
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Lifecycle/damage:
White pine weevils overwinter as adults under dropped needles and other ground debris, usually close to previously 50-70°F. Adults will crawl and sometimes fly to trees to mate and to feed for a period of time. Soon, females will lay eggs by chewing small pits in the bark, beginning just below the unemerged bud of the new terminal leader on top of the tree. A single female may lay 100 or more eggs.
Larvae grubs then begin to feed and tunnel into the wood underneath the bark, ultimately girdling the tree, causing the new terminal growth to wilt and die. This wilted new growth resembles a “shepherd's crook” that is easy to identify. Needles will also become light in color and eventually die and drop. Larvae can also tunnel downward far enough to damage prior-season growth. Shoot regrowth from buds below the dead leader results in forked trees with competing leaders. Repeated attacks of these secondary leaders will then result in stunted, bushy-topped trees.
Management:
Pruning-Pruning out infested leaders can be used to reduce white pine weevil populations. Timing is critical and needs to be done between when leaders show evidence of infestation (wilting) and when the insect emerges from the leader as evidenced by exit holes (Fig. 4). The pruned material should be removed and disposed of since weevils may still develop in prunings. Soil Treatments- Soil drench/injection treatments with systemic insecticides can prevent white pine weevil injury. These applications are best in the fall to allow sufficient uptake by the tree by springtime. Spray applications- Spray insecticides in spring so that they cover the tops of the trees where adults would be active. Treatments should be made when adults are just beginning to feed and lay eggs. Inspections for adults should begin in early spring when temperatures are consistently over 50°F. Adults are hard to find, so thorough inspections are necessary.
For more information about the white pine beetle and recommendations, you may stop by our office or schedule a free consultation. Remember, if you plan on using any kind of pesticide, please read and follow the label!
