As we prepare for another season of Fall Tree Wellness, another important insect to take note of is White Pine Weevil. White Pine Weevil is a damaging pest to a broad range of conifers, including White, Scotch, Red and Austrian pine as well as Colorado blue, Norway, and Serbian spruce. Douglas-fir can also be attacked. White pine Weevil does the bulk of its damage to trees in the later part of the Spring, but I mention it now because we get the most successful management of this pest with a Fall application of systemic insecticide. If you have had damage from White pine weevil in the past - now is the time to take corrective action.
Adult white pine weevil spends the winter underneath dropped needles and debris, generally very close to previously infested trees. On warm days in early Spring, the adults travel to the terminal leaders of host trees and begin feeding on terminal branches. Later in Spring the adult females will mate and deposit eggs into feeding wounds. Dozens to hundreds of eggs can be deposited into one terminal leader. Eggs hatch one to two weeks later with larvae feeding downward on the inner bark of the terminal stems. Feeding continues through mid-July at which point larvae pupate in hollowed out chambers inside the stem. New adults emerge in late July - August and feed intermittently on small twigs throughout the canopy of the tree until they move to the base of the tree for overwintering shelter.
The most destructive stage of white pine weevil is the larval feeding stage which produces a conspicuous injury to the host tree by causing the new growth of the tree to wilt and die back. The affected terminal shoots wilt into a “shepherd’s crook” (see below photo) and the needles turn lighter in color before turning brown and eventually falling off. In most cases host trees are not killed. However, feeding injury stunts the growth of the tree and can also cause trees to develop poor structure with multiple new leaders forming beneath damaged areas.
Injury to white pine is generally confined to the previous season’s growth. Damage on Scotch pine and spruce will often extend downward through two or three year’s growth.
Examples of the “shepherd’s crook”
Managing The White Pine Weevil
Host plants are most attractive to White pine weevil between 3’ and 20’ in height. In June - July, look for curled or dead terminal leaders that have the appearance of a “shepherd’s crook.” These infested leaders should be pruned out of the tree and destroyed or removed from the site to attempt to eradicate the pest from the host plant.
If you have had infestations of white pine weevil in the past or have host plants in the preferred size range, a well-timed soil drench with an appropriately labeled systemic insecticide works really well at controlling this pest. This application is recommended in the Fall to allow sufficient time for uptake of the insecticide to the terminal shoots of the tree by Spring when larval feeding resumes.
TJ Nagel | Regional Manager, Russell Tree Experts
ISA Certified Arborist® OH-6298A // Graduated from The Ohio State University in 2012, Earned B.S. in Agriculture with a major in Landscape Horticulture and minor in Entomology // Tree Risk Assessment Qualified (TRAQ) // Russell Tree Experts Arborist Since 2010