The white pine weevil, one of the most destructive pests of the eastern white pine in Pennsylvania, kills the tops of many different types of conifers. Although it attacks mostly pines, it can also be found in spruce and fir trees. Several generations of this pest can severely reduce the aesthetic value of their host.
White pine weevils spend the winter as adults in dropped needles under or near host trees. As days warm up in March or April they will fly or crawl to the leaders of suitable hosts. They begin feeding on the bark of terminal leaders. Mating occurs on the bark of the tree through most of June. A single female may lay 100 or more eggs in pits on the bark of the previous year’s leader. After hatching, grubs tunnel downward under the bark. Adult beetles emerge from late June to early September. After emergence, the beetles fly to other areas.
Between the feeding and the egg laying, the top 18-24″ of the leader is usually killed. Severe infestation may result in the loss of 2-3 years of growth. Glistening drops of resin oozing from holes in the leader are the first signs of attack, caused by adult weevils that are feeding before egg-laying. As the terminal is girdled, the new shoot of the current year’s growth withers and the tip bends over and turns brown. This stage of damage usually becomes noticeable in July. These infested leaders should be pruned at a point below the tunneling grubs, making sure to either burn or secure them in plastic trash bags and remove them from the property. If left on site the weevils may continue to develop in the prunings.
The standard treatment for pine weevil is to spray insecticides such as permethrin, bifenthrin or cyfluthrin at different intervals, but timing of these spray treatments is critical. The first application, to the terminal leader, as well as the lower trunk of the tree, must be done right before the adults begin feeding and laying eggs. A second spray treatment should be done a few of weeks later to protect the terminal leader. Other applications to the leader during midsummer are often necessary to manage this insect during outbreaks.
As an alternative, a single systemic soil injection of Imidacloprid can be applied in the fall to avoid multiple spray applications throughout the season. This allows adequate time for the chemical to be taken up to the terminal leaders of the tree. This method of control uses less active ingredient of chemical overall and has a lower environmental risk. It also has a reduced impact on natural enemies of the weevil.