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Trees and Their Enemies
3/1/2008
Linda Langelo
Horticulture Program
Coordinator
Colorado State University Extension
Golden Plains
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Every type of tree variety has a specific insect vector that is
attracted to it when a tree becomes stressed. There are times when borers enter
trees because of an open wound or exposed decaying cambium from improper
pruning or breakage during a storm. The cambium is a thin layer of cells which
are constantly dividing and forming new wood which in turn increases the girth
of the tree. Sometimes a particular insect vector can attack more than one type
of tree variety.
Cottonwoods, ash, elm and other hardwoods can attract
the carpenterworm. These larvae tunnel into the sapwood which continues further
inside the tree behind the active cambium layer. These carpenterworms go deeper
into the tree's center called the heartwood. Trees heavily infested may break
large limbs during high wind storms. Trees may also appear gnarled and
misshapen when the vector has chronically infested these trees. This is common
in "shelterbelts"or windbreaks in Eastern Colorado. The one most distinguishing
characteristic from other borers is an exterior opening in the bark of the tree
by which it expels sawdust. The larvae can reach three inches in maturity. The
adults are moths which appear as adults in May. The moths have stout bodies
with grayish-mottled forewings.
This is one of the many different types
of borers. Borers can be beetles and moths. But the important thing to keep in
mind is that they do the most damage in their larval stage. Just like children,
they need food to grow. They can eat a lot in one season for some, but with
others like the cottonwood borer, a beetle, takes two seasons to complete their
lifecycle.
Cottonwood borers, beetles of an inch and a half long with
yellow and black markings feed in the bark and down into the larger roots the
first fall. The second season they tunnel into the galleries of the tree base.
Trees like willows, cottonwoods and poplars tend to attract this insect.
Mostly, this insect occurs in southeastern Colorado.
Pole borers are a
reddish-brown beetle about three-quarters of an inch long which enters where
the cambium is exposed to the environment. After several attacks the insect is
associated with a wood fungus. The key is they come to damaged or wounded sites
on the tree which attains high moisture content. Again, trees can break off
limbs in high wind storms. These insects get their name from the telephone
poles or other poles having their bases covered with soil. These pole borers
take up to three years to complete their lifecycle.
What does one look
for when inspecting their trees in spring? First see if there are any exit
holes and fresh sawdust. Second, look for sap or pitch either in the crotches
of branches or on the bark of the trunk. Third, look for swellings on larger
branches and sometimes even on the trunk. Fourth, look for bark at the base of
the tree that peels off easily. If there are tunnels immediately behind the
bark, the tree may have borers. Identification is necessary with the adult
stage of the insect. The larval stage is the most difficult to distinguish
between these insects. If you would like more detailed information on the
different types of borers for Eastern Colorado, go on-line to Colorado State
University Extension Website. There is a fact sheet titled Shade Tree Borers
and number 5.530. Since there are so many different types, it makes it too
numerous to place in one article. There are colored pictures on the fact sheet
which will be of help, if you happen to see a problem and spot an insect of
this type.
Treatments vary according to the family in which the insect
is classified. There are some borers in the butterfly family and some in the
beetle family. Certain chemicals are more effective with the beetle family.
First and foremost, the identification of the insect must be made
before determining a solution to the problem.
Keeping trees properly
watered will help a tree with its own immune system. Water carries nutrients
throughout the vessels of the tree. Water helps the tree produce proteins and
enzymes. Without water, the tree stops actively growing. This is similar to
humans. Without water for humans, our body stops functioning.
Without
the proper amount of water a tree can survive, but it may not be surviving in a
healthy way.
Borers are most effectively taken care of by prevention. It
is difficult to know if borers are present unless you see some sort of pitch on
the bark or an exit hole in the tree. And by that time, a significant amount of
damage can be done. Borers are the trees' cancer. They are silent, but deadly
and until the damage has advanced no one but the tree knows they are present.
If you have any questions or concerns, please call your local Extension
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Page Created and Maintained by: Perry D. Brewer, Area
Extension Agent (Technology Education/Youth)
7/17/2008 |
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