Foresters try to locate and dispose of all the diseased trees in
the State and Government forests. They strive to remove all the
sources of tree disease from the woods. They can grow healthy
trees if all disease germs are kept away from the timberlands.
Some tree diseases have become established so strongly in forest
regions that it is almost impossible to drive them out. For
example, chestnut blight is a fungous disease that is killing
many of our most valuable chestnut trees. The fungi of this
disease worm their way through the holes in the bark of the
trees, and spread around the trunk. Diseased patches or cankers
form on the limbs or trunk of the tree. After the canker forms on
the trunk, the tree soon dies. Chestnut blight has killed most of
the chestnut trees in New York and Pennsylvania. It is now active
in Virginia and West Virginia and is working its way down into
North and South Carolina.

[Illustration: SECTION OF A VIRGIN FOREST]

Diseased trees are a menace to the forest. They rob the healthy
trees of space, light and food. That is why it is necessary to
remove them as soon as they are discovered. In the smaller and
older forests of Europe, tree surgery and doctoring are practised
widely. Wounds are treated and cured and the trees are pruned and
sprayed at regular intervals. In our extensive woods such
practices are too expensive. All the foresters can do is to cut
down the sick trees in order to save the ones that are sound.

There is a big difference between tree damages caused by forest
insects and those caused by forest fungi and mistletoe. The