The flatheaded apple tree borer, _Chrysobothris femorata_ (Oliv.), and
other species of flatheaded borers attack unhealthy or recently
transplanted pecan trees by burrowing in the bark and sapwood of the
large branches and trunk. Their presence is indicated by the appearance
of darkened, depressed areas in the bark from which traces of frass may
protrude. When these portions of the bark are removed, shallow winding
burrows packed with sawdust may be observed. The burrows usually are on
the sunny side of the trunk or branch, but may extend completely around
and penetrate the wood to a depth of 2 inches. Young trees may be
girdled by this insect.
The adult beetle is about one-half inch long, broad and blunt at the
head end and tapering to a point posteriorly. Its wing covers, which
have a metallic sheen, are dark colored and corrugated.
The larva, or borer, which is legless and yellowish white, attains a
length of 1¼ inches when full grown. Immediately behind the head is a
broad, flattened expanded area from which the insect takes its name.
The winter is passed by larvae in varying stages of development within
the tree. In the spring, they change to pupae in their burrows, emerging
as adults during the spring and summer. The female beetles deposit their
eggs in cracks or bruises in the bark. The larvae which hatch from these
eggs feed during the remainder of the season and pass the winter. There
is only one generation each year.
[Illustration: Figure 22. Adult twig girdler and characteristic
injury to twig.]
_Control._—The beetles are attracted to trees or areas of trees in a
devitalized condition, induced by transplanting, drouth, sunscald,
bruises or poor growing conditions. The trees must be kept in a healthy,
vigorous condition by proper fertilization and watering. On young or
transplanted trees, wrapping the trunks in early spring before the
adults appear is the only effective control known for these insects.
Injury can be prevented by thoroughly wrapping the entire trunk from
ground level to the branches with heavy paper or other wrapping
material. The wrapping should be tied securely with twine and should be
maintained on the tree for 2 years. Regular observations should be made
to see that the twine does not girdle the tree.
In older trees, the borers can be removed with a sharp knife. Care
should be taken to injure as little of the healthy wood as possible. If
the wound is extensive, it should be trimmed and then painted with a
commercial tree paint or with a mixture of one part creosote and three
parts coal tar. Dead and dying limbs and trees should be removed from
the orchard each year and burned before the following spring. If they
are not burned, the borers in them may mature and re-infest surrounding
trees. Commercial tree borer preparations are of little value in
controlling this insect.