By Megan Gross, Horticulture/Natural Resources Extension Agent, Colorado State University Cooperative Extension
Landscape trees are not cheap. Nor are they guaranteed to stand up against the various stresses imposed upon them by nature and owner (sorry folks). In our area, a trees greatest threat is usually lack of moisture. Occasionally, however, an aggressive insect or disease compounds a trees daily dose of stress.
White pine weevil does just that to spruce trees.
White pine weevil (Pissodes strobi) is a seldom seen insect that looks like a small, black beetle with a disproportionately long snout. In the early spring, just after the snow melts and temperatures begin to rise, the adult female weevil awakens from her dormant state. She hikes it up the trunk of a spruce and lays eggs at the base of the leader (the uppermost branch of the tree responsible for upward growth). The eggs hatch into larvae (1/4 inch piece of white rice with a brown head) and the larvae bore into the leader and feed.
Symptoms are first noticeable around mid-June. The top of the tree curls and seems to be wilting. Eventually the leader and sometimes uppermost lateral branches turn brown and drop needles.
Damage at top of tree
The adults emerge in late summer, excavating 1/8" exit holes. Adults stay within the same tree, feeding on needles, buds and twigs for several weeks before reverting to the base of the tree for overwintering. You may notice minor chewing injury to buds if infestations are severe.
White Pine Weevil exit holes
If your spruce is showing symptoms of white pine weevil, remove the infected/dead leader and train your next best lateral to take over the leader (upright) position. You can do this with a wooden stake and some string. Destroy or rid infested leaders, as weevils can survive in them.
As soon as the snow melts in the spring (early March to late April, depending on where you live), spray your healthy leader with carbaryl (Sevin). You will probably want to do one repeat application according to the label. Sevin PROTECTS the tree from the weevil; once the larvae are feeding, they are protected from insecticides. I have not been able to find any information on an organic alternative to using carbaryl to protect trees from this insect pest.
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010