Q: We have a grouping of pine trees in our backyard, planted over the last 1 to 4 years. The trees are now 4 to 10 feet tall. It seems like every year, one or more trees (especially the white pines) lose the leaders. The top few branches turn brown and die out. The rest of the tree remains healthy. Is there something we can do to prevent this?
A: It could be one of several things, but Ill put my money on the white pine weevil. The dastardly larvae of this insect feed just under the bark of pine leaders and branch tips high on the trees. White pine is the favorite, although these weevils also like spruce, most other pines and even an occasional Douglas fir.
Check the leaders and tips in early to mid-April for fresh sap and a droopy appearance. This is when adult weevils crawl up the trees and gnaw into the bark in preparation to lay eggs. Eggs hatch in a week or so, and the white, C-shaped, legless larvae with brown heads start feeding on the wood. You usually wont notice the problem until early summer when the tips have browned and died. But by mid-July, the larvae have matured into young adults, which do some further feeding on branches but not as deadly as the larvaes tip feeding.
To prevent new trouble, snip off and discard tips where youve discovered feeding larvae in April or May. Or spray at the first sign of that April sap, using an insecticide labeled for pine weevil control. (Bifenthrin and pyrethrins are two suggested by Penn State University.) If you nip this problem in the bud, so to speak, surrounding healthy branches should take over and help the trees growth habit to recover.