Controlling white pine weevil
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Larvae of the white pine weevil kill the terminal leader and the top two to four years of growth on many varieties of spruce, as well as white and Scotch pine trees. If you had weevil damage last year and you need to control the weevils, you will have to do it early this spring.
The adult weevils overwinter on the ground, protected and insulated by the litter (fallen needles). Once they warm up, the weevils move up to the tops of the trees in the late afternoon or early evening and feed on the terminal leader. Each time a female weevil makes a feeding wound on the terminal, she lays one to four eggs in the wound. Those eggs will hatch within a few weeks and the larvae chew their way through the bark. They will feed in the phloem under the bark for several weeks, pupate and then emerge as new adults around midsummer.
If you need to control white pine weevil, your one opportunity is early in the spring. Insecticide should be applied to the terminal leader once it begins to warm up - somewhere around 25-65 GDD50. It’s better to be a bit early than to be late with this application. Use a persistent product, because the adult weevils don’t all warm up at the same rate. You could have weevil adults feeding on the terminals for three weeks or perhaps longer. If you can avoid spraying the rest of the tree, you will conserve beneficial species like predatory mites.
Growers in Pennsylvania have had luck using tedder traps to detect white pine weevil adults. These traps are placed in the field next to trees that was damaged the previous year. Weevils overwintering at the bases of the trees are attracted by the scents of alcohol and turpentine that mimic the odor of pine trees. Information on these traps can be found at http://ctrees.cas.psu.edu/info_insects.htm#Insects
Dr. McCullough’s work is funded in part by MSU‘s AgBioResearch.