Weevil control

Asked June 17, 2020, 5:15 PM EDT

A few of our spruce trees are infested by weevil: leaders yellow and wilted. We have called Apex Pest control since early May but they have not come to spray the trees. The questions are: 1. Is it too late now (6/17) to spray ? Apparently this needs to be done before the weevils lay eggs? 2. If spraying now is not effective then what can we do now to stop infestastion in the same trees and neighboring trees? what pesticides to use? Thank you

Lincoln County Wyoming

3 Responses

Is the weevil that you are dealing with the white pine weevil (Pissodes strobi) that feeds under the bark on the upper leaders of the conifer trees and that cause a "shepherds crook" to form and kills the new growth? If that is the pest, then it is too late to spray topical insecticides on the trees to prevent the weevils from putting the next generation of eggs under the bark. If your trees are short enough you can examine the leaders, you will see clear drops of pitch oozing from the tiny holes they chew in the bark to put their eggs in.

This information from Michigan State Univ. advises people to examine the tree's upper leaders during the growing season and remove and destroy them when they start to die to kill the larvae before the end of July. https://www.canr.msu.edu/news/timing_is_critical_for_white_pine_weevil_control
The adults of white pine weevils emerge in the early spring and you can get traps to monitor for the adult weevil emergence from the ground, where they spend the winter, next spring.
It may be too late to spray typical contact insecticide on the trees but, if the damage in the terminal growth is not too advanced, you may get suppression with the systemic insecticide applied as a soil drench or a bark spray now. Dinotefuran (Safari or Xylam) might still work this summer. Of the available systemics it translocates pretty quickly. Here is a Montana State University bulletin on this pest's management and dintoefuran is listed as a chemical control option
https://apps.msuextension.org/documents/UA_Files/insect_fact_sheet_white_pine_weevil.pdf

Thank you for your prompt response.
Yes white pine weevils is what we have.
A few more clarifications please:
1. Is it OK to apply systemic Imidacloprid drench now - before July - or does it have to be Dinotefuran?
2. If applied in the fall, what is the latest date (best dates range / temperatures range for Lincoln County WY) Imidacloprid can be applied for it to be effective ( to be sucked up in the tree)
3. Both these chemicals list Black vine weevils Otiorhynchus sulcatus but not white pine weevils Pissodes strobi - I guess if all extension services recommend these then they're good - just making sure.

Thank you,

Nhu





Dear Nhu:

For application an now, in an effort to try and stop the damage the current generation of white pine weevil larvae is inflicting on the tree the dinotefuran products are moved the most rapidly by the trees. Imidacloprid can be applied in the fall before the ground freezes to allow time for the tree to uptake it into its tissues so the larvae will be controlled next spring. It would then last through the spring and summer. The dinotefuran can also be applied early next spring to provide the same protection. On page 14 of the full Safari 20SG label in the "Ornamental plants and Forest" crop, in the "application to soil" soil table white pine weevil is the last pest listed in the cell.