Dieback due to white pine weevil larva feeding.

Noticing a wilted leader on pines or spruces?  White pine weevil is likely the culprit. Although it’s almost officially summer when the symptoms are first noticed it all started back in the early spring when, on a warm day in March- April, the female weevil lays her tiny eggs a few inches below the terminal bud. Those eggs soon hatch and the young larvae start to consume the stem’s vascular tissue.    With the loss of this vascular pipework the tree’s terminal leader wilts and brown dieback soon becomes visible.

With the bark peeled back, a white pine weevil larva is visible inside spruce leader.

In late July and August adult weevils emerge through small holes they carved at the base of the dead terminal.  After the adult weevils emerge they enter leaf liter and are not seen until March of the following year.  If you prune out and destroy the affected leaders before the holes appear and the adults emerge (Late June to mid-July for most of New York) you can reduce numbers of adults that will lay next year’s eggs.

Exit holes of at base of area damaged by White Pine Weevils. Prune and destroy before these are visible.

A blue spruce disfigured due to a missing leader caused by White Pine Weevil damage.

White pine weevil is one of the earliest pests we treat for in the spring.  Knowing when to treat can be tricky.  Using growing degree days in the spring can be helpful to prevent damage.  

See the Insect Section of Pest Management Guide for Commercial Production and Maintenance of Trees and Shrubs for growing degree day target window for treatment  and other control information.