Damage to terminal leader of an understory white pine in Portage County. / Photo Credit: Wisconsin DNR

By Alex Hornung, DNR Forest Health specialist, Plover
Alexandra.Hornung@wisconsin.gov

This is a great time of year to be looking for or observing damage from the white pine weevil.

The insect is native and causes terminal leader mortality in susceptible species. Despite the name, there are numerous species of trees that are attacked in addition to white pine, including Norway spruce, jack pine, white spruce and many more.

The damage from white pine weevil is more evident when the needles on the main leader are still attached and are brown in color, primarily in the month of July through the winter of the year that the damage occurred. It is more difficult to see previous years’ damage, because the needles fall off and the dead terminal leader will either snap off or be bare. When the leader is killed, the branches below will grow in place of that leader and will eventually correct by self-selecting a new leader.

Chip cocoons and a larva are found inside the killed terminal leader of a white pine tree. / Photo Credit: Wisconsin DNR

Every year, reports come out of the northern and central zone of damage, sometimes reaching 20% or more in pine/spruce plantings where trees are open-grown. An increased number of reports in plantings have been coming out of the central zone throughout this field season. This may be due to an increase in populations of the weevil this year, or a simple function of thriving plantings that have robust terminal leaders more susceptible to attack.

In forested stands, pesticides are not the primary method of control due to practicality and cost. Trees will very often self-correct, and natural predators will do better when there is an adequate population of the weevil to sustain them. Impacted trees may end up with a noticeable crook in the stem as they continue to grow. These trees can be targeted for removal during regularly scheduled thinnings as the trees mature.

Terminal leader damage is evident on planted white pine and spruce trees in Waushara County. / Photo Credit: Wisconsin DNR

For more information about white pine weevil in Wisconsin, please refer to this article from 2023, written by Linda Williams, Wisconsin Department of Natural Resources Forest Health specialist for the Northeast zone.