The white pine weevil, Pissodes strobi, is a key pest in conifer production. This is primarily due to its feeding damage to the terminal of conifers causing flagging and dieback. It most commonly attacks spruce in nursery production in the PNW.
Description
White pine weevil larvae are white, c-shaped grubs with a brown head capsule. White pine weevil adults are black with reddish-brown and white spots on the elytra and a long black snout from which their bent antennae arise. They have fully-functioning wings.
Damage
Adults feed on the terminals, chewing through the bark. Small punctures and sap on the terminals are evidence their feeding damage. They oviposit (deposit eggs) into these feeding wounds . The larvae hatch from these eggs, feeding in the cambial tissue under the bark, causing characteristic wilting, and eventual death of the terminal.
The weevil larvae pupate in pupal chambers lined with sawdust under the bark and emerge as adults in mid-late summer. The adults feed in the trees until they return to the duff at the base of the tree to overwinter. There is one generation a year.
Monitoring
In the early spring, monitor for adult weevils that have emerged from the duff at the base of trees. Michigan State University Extension recommends the use of Tedder traps to trap the adult weevils as they emerge. They mention they begin trapping adult weevils at 35 GDD50 (35 accummulated Degree Days at using a base of 50 degrees Fahrenheit). Research in Pennsylvania showed emergence once soil temperatures in the top two inches were 50 degrees Fahrenheit or 10C. Ohio State's Phenological Indicator site has adult emergence at 84 degree days and nearby phenological indicators are first bloom of star magnolia and first bloom of border forsythia.
Cultural Management
Cut out damaged terminals and remove these prunings from the nursery.
Chemical Management
Chemical management is timed to prevent successful oviposition by the winged adult weevils that feed and oviposit in the spring. An insecticide application is applied to the terminals of the trees.
For chemical recommendations, check the nursery section at the PNW Insect Management Handbook.
Additional Web Resources
White pine weevil. USDA Forest Service Forest Insect & Disease Leaflet 21 (pdf). A very thorough presentation on the biology, ecology, and management of white pine weevil with good images. The emphasis is silviculture but much pertains to nurseries.
The White Pine Weevil. Colorado State University
White Pine Weevil Fact Sheet. Penn State Woody Ornamental Integrated Pest Management
Gardosik, S. and R. Leyman. 2005. White Pine Weevil Detection Traps. PA Department of Agriculture. Instructions on how to use Tedder traps for detection of white pine weevil adult emergence.
Accessed 31 March 2012.
Wilson, R. and E. Bechinski. Management of White Pine Weevil in Spruce. <4 March 2016>
Original version: <6 June 2007)
Last revision <15 February 2018>
Author: R.L. Rosetta, Extension Nursery Integrated Pest Management, Department of Horticulture, Oregon State University/NWREC.
White pine weevil adult newly emerged from pupal chamber.
White pine weevil adults
Wilting and crookneck symptoms from white pine weevil on blue spruce
Late symptoms of white pine weevil damage on blue spruce
Further wilting and crookneck symptoms from white pine weevil on blue spruce
Early symptoms of damage from white pine weevil on blue spruce
Early and late symptoms from white pine weevil on blue spruce
White pine weevil egg
White pine weevil lavae in pupal chambers
White pine weevil lava in pupal chamber
White pine weevil larva
The easily peeled-back bark reveals numerous larvae
White pine weevil larvae under the loose bark
White pine weevil oviposition holes