Q.
I have a pine tree that seems to be dying at the top. It is fairly
tall, and I cannot see what is happening up there. I noticed that
some of my neighbors' pine trees look the same. Is there some kind
of blight or something hitting pine trees? Is it going to kill the
tree, or can I do something to save it?
A.
Judging from your description and the digital photo attached to your
question, an insect called the white pine weevil is responsible for
the damage to the top, or terminal leader, of your Norway spruce.
White pine weevil damage will not kill your spruce, but it can
destroy the natural shape of the tree.
This pest is a
small (1/4-inch long) reddish-brown beetle
with white spots on the ends of its wing covers and an elongated
snout. White pine weevils overwinter as adults in leaf litter and
other debris on the ground. As the weather warms in spring, they
migrate to the leaders of white pines, Norway and Colorado spruces
(and other susceptible trees), where they mate. Adult females bore
out a circular cavity and deposit anywhere from one to five eggs.
Hundreds of eggs can be laid in a single leader.
Once the eggs
hatch, the larvae bore into the leader to feed. Their feeding
activity cuts off the flow of water and nutrients through the stem,
which causes it to wilt and die. New growth usually sprouts below
the dead leader, but the damage destroys the shape of the tree. The
larvae pupate and hatch out as adults by late summer. They drop to
the ground to overwinter and the cycle starts over again.
White Pine is a popular landscape tree
To protect
undamaged trees, direct your control efforts at the adult females as
they lay eggs. Begin scouting for white pine weevil activity as the
weather warms in spring, from mid-March through mid-April. When the
females begin laying eggs, you will see resin oozing from the
punctures she makes to lay her eggs (binoculars can be a big help if
you have a large tree). Only the terminal leader needs to be sprayed
to protect against white pine weevil damage.
Unfortunately,
there are no insecticides on the market that are available to home
gardeners. A licensed pesticide applicator can spray your tree for
you. Since your tree is large, it is probably a good idea to hire
someone with the training and equipment to spray it safely and
thoroughly.
Another control
option is to prune out the infested leader and physically remove the
larvae from the tree. This will reduce the number of overwintering
adults and perhaps protect your tree 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 become the new
terminal. Try to tie it into an upright position with wide,
nonbinding 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 near the leader to preserve the shape of the
tree.
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