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Picture of the Week
for 8 August 2000

White Pine Weevil

Cliff Sadof, Entomologist

White Pine Weevil Damage
White Pine Weevil Damage
(Click on the small image to view a larger image.)

White pine weevils have been fairly abundant this year. These weevils cause the upper most shoots of white pines to curl into an S-shape or shepherd's crook. The injury can be distinguished from Zimmerman pine moth in that there is no accumulation of gummy sap at the junction of the tree branches in the main stem.

Adults are emerging now from the pine trees. Now is a great time to spray trees with Dursban, Lindane, Astro, or Talstar, to kill adults that feed on trees. It is too late to prune out infested leaders. Homeowners can use Lindane and Dursban.

Some background: White pine weevil Pissodes strobi (Peck) (20)
Order and Family: Coleoptera: Curculionidae
Hosts: Pines, especially white pine, Norway, and Colorado Blue Spruce.

Damage and Diagnosis: Infested trees have the leader curled into a shape that resembles a shepherd's crook. Lateral branches from the infested tree's first whorl may also be curled. The top two to 3 years of growth can be affected. In early summer, legless (1/4") white c-shaped grubs can be found in stems, beneath the bark surface or in the stem.

Biology: Adults winter in leaf litter and fly to tree tops to mate when the weather warms in the spring. Females lay many eggs in terminals that hatch into grubs that bore into shoots. Legless larvae continue to feed until July when they pupate in chip bark cocoons. Adults emerge in August and chew on twigs.

Control: Prune and destroy damaged leaders that contain larvae or chip bark cocoons before adults emerge. Applications of broad spectrum insecticide to tree tops should be timed to kill adults gathering on twigs in early spring (April), or adults feeding on twigs in August. Mixed species plantings of pines are less likely to build damaging numbers of this pest than pure stands of susceptible species.

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Last updated: 9 April 2002/tlm.
The Plant & Pest Diagnostic Laboratory at Purdue University.