Larvae from the white pine weevil, Pissodes strobi, has caused damage which has become very apparent in recent weeks. Larvae had begun feeding late April on the terminal leaders and the damage is very evident on eastern white pine, Douglas fir, Norway spruce, Siberian spruce and Colorado blue spruce. Larvae will have pupated and adults emerged by late spring or early summer. If the terminal leader becomes heavily infested, larvae feed side by side encircling the stems. Once the terminal leader becomes stunted and wilted it may be too late to save it, consult your arborist about what to do if you see this damage. Adults overwinter in the leaf litter beneath trees, prior to egg production adults chew holes near terminal bud and central leader which results in a distinctive pitch flow which whitens when dry. Eggs are laid in the holes which are pretty protected within the top foot of the central lead. Control of white pine weevil larvae is dependent on treating adult females prior to egg laying. This can be difficult due to timing; the optimal window for control is between 7 and 58 growing degree days, typically during March or April. For much of the region this is still very early spring, when we are still applying fertilizers and dormant oil treatments.
Pruning of damaged leaders and laterals may be beneficial, timing and technique will be essential, so consult with your arborist should you suspect white pine weevil on any of your landscape trees. A “shepherd’s crook” may be visible prior to the dieback of leaders or lateral branches, but by late spring or early summer the larval feeding will have destroyed the water conducting tissue. Older trees having 20 or more feet in height will be more resistant to this pest due to the development of multiple leaders.