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Pine tree dieback

Weevils can cause dead tips on pine trees

By: Sandy Feather ©2011
Penn State Extension


Q. I have a windbreak of white pine trees that seems to be dying from the top down. I really value these trees and do not want to loose them. Do you have any suggestions for saving my pine trees?
  
  A. Judging from your photos and description, an insect called Pissodes strobi or White Pine Weevil is responsible for the damage to the tops of your white pine trees. While white pine weevil damage is not likely kill your trees, it can destroy their natural shape. Although weevils feed primarily in last year’s growth, their feeding activity can kill the top two or three whirls (tiers) of branches. In addition to attacking white pines, this pest damages the tops of other pine species, spruce and Douglas Fir.
  

Douglas Fir
Douglas Fir tips can be attacked
by White Pine Weevil

This 1/4-inch long pest is a reddish-brown beetle with an elongated snout and white spots on the ends of its wing covers. White pine weevils overwinter in leaf litter on the ground as adults. As spring weather warms up, they migrate to the terminal leaders (topmost growth of your pines) on susceptible trees where they mate. Adult females can lay hundreds of eggs in a single leader, where they bore out a circular cavity. They usually deposit one to five eggs per cavity.

After the Eggs Hatch

Once eggs hatch, weevil larvae bore into the leader of the tree to feed. Their feeding activity cuts off the flow of water and nutrients through the stem, which causes the tip to wilt and die. New growth usually sprouts from below the dead leader, but the resulting damage destroys the shape of the tree. These larvae pupate and hatch out as adults by late summer and drop to the ground to overwinter.

Cultural Controls

A non-chemical control option is to prune out the infested leaders and physically remove the larvae from the trees. This will reduce the number of overwintering adults and help protect your trees from further damage. It is best done as soon as the leader droops, often in early June. Prune the infested leader out just below where the bark is discolored and discard it by sealing it tightly in a trash bag or burning it immediately. There should be a flush of new growth at the base of the dead terminal. You can select the most upright shoot of this new growth to replace the dead terminal. You can try to tie it into an upright position with wide, non-binding masking tape or the plastic tape used to stake tall flowers. Remove all ties after one growing season. Prune out the rest of the new growth at that whirl to preserve the shape of the tree.

White Pine
A good shape is important for
white pine Christmas trees

Home gardeners can use a systemic insecticide containing imidacloprid, including Bayer Advanced Tree and Shrub Insect Control II, Monterey Once-a-Year Insect Control, and Bonide Annual Tree & Shrub Insect Control. Applications should be made in fall to allow enough time for the product to be absorbed by the roots and taken up to the terminal of the tree. It is important to rake back any mulch or accumulation of pine needles so you apply the product to bare soil within 18 – 24 inches of the trunk. It is also important that the soil is moist, but not saturated at the time of application. Water it in according to label directions after application and replace the mulch.

Chemical Controls

Other chemical control measures are directed toward adult white pine weevils as they begin feeding and laying eggs in early spring. Resin oozes from the punctures they make in the terminal leaders. Scout for this symptom from mid-March to April, using binoculars to examine the tops of tall trees. Adult controls should be applied to the terminals when you start seeing resin droplets. There is no need to spray the rest of the tree. Unfortunately, there are no insecticides on the market to control white pine weevil adults available to home gardeners. A licensed pesticide applicator can spray your trees for you. Since your trees are large, it is probably a good idea to hire someone with the training and equipment to spray them safely and thoroughly.
   

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