Aaaack! White Pine Weevil

posted by Ron Wilson - 

Article supplied by Buggy Joe Boggs and re-printed with permission

White Pine Weevil (Pissodes strobi) is one of our sneakiest conifer pests found in Ohio. Females spend the winter out of sight cooling their six heels in the duff beneath their pine or spruce targets. As temperatures warm in the spring, they climb their hosts to feed and lay eggs in the terminals. Sap oozing from small holes in the terminals is a calling card of this weevil.

 

This native weevil has a wide conifer host range that includes Scotch, jack, red, pitch, and eastern white pines as well as Douglas-fir and all spruces. Indeed, the weevil's love of spruce is exemplified by its alternate common name, Engelmann Spruce Weevil, or simply Spruce Weevil. White pine weevil is not just found in Ohio; it ranges from the east coast west into the Rockies.

 

Overwintered female emergence commences when the accumulated Growing Degree Days (GDD) reach 84. This roughly coincides with the full bloom of Northern Lights Forsythia (Forsythia x intermedia), Speckled Alder (Alnus incana), and Cornelian Cherry Dogwood (Cornus mas). Although we've surpassed the magic GDD number of 84 in southern Ohio, and I've taken some wonderful pictures of Cornelian Cherry blooms, it doesn't mean all is lost. The roller coaster pattern of our spring temperatures mean that we keep hitting the pause button on weevil activity.

Of course, the clock is ticking with executing the first suppression tool for the season: applying a "borer spray" to protect conifer terminals against this weevil. Females use their chewing mouthparts located at the tip of their long snout (rostrum) to chew small holes through the bark to feed on the sugar and nutrient rich phloem. Eventually, they turn around and deposit an egg in some of these holes.

 

Targeting the terminals with an insecticide to kill the females will prevent the egg laying activity. Effective products include those based on the active ingredients bifenthrin (e.g. Onyx), permethrin (e.g. Astro), or cyfluthrin (e.g. Tempo). A second application may be required depending on spring weather conditions and product label recommendations.

 

If females are successful with laying eggs, the resulting white, legless, slightly curved, grub-like larvae tunnel downward side-by-side just beneath the bark feeding on the phloem. The larvae will eventually construct so-called "chip cocoons" in which they pupate.

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