research
programs were started early in Wisconsin and Iowa. Neighboring states
were quick to follow as surveys showed a wider distribution of the
disease. Now almost every state in which oak wilt occurs is taking part
in efforts to learn more about the disease and its causal agent so that
practical control measures may be applied before the spread of the
disease gets out of hand. The National Oak Wilt Research Committee at
Memphis, Tennessee, supports in part an intensive oak wilt research
program in coordination with several midwestern universities and with
the U.S.D.A., Bureau of Forest Pathology.

Until recently the causal fungus of oak wilt was known only in its
asexual or imperfect form living in the sap stream of infected trees.
The most important question to be answered now is how the fungus
spreads over long distances from diseased to healthy trees. Before this
could be accomplished, however, we had to know how the fungus escapes
from the inside to the outside of diseased trees where it can be exposed
to agents of dissemination.

In the late summer of 1951 clearly visible mycelial mats of the oak wilt
fungus were found in Illinois under the loose bark of wilt-killed trees.
These mats were usually located beneath cracks in the bark; thus, they
were exposed to the outside air and to visiting insects. Most
wilt-killed trees contain beneath the bark numerous insect larvae of
wood and bark boring beetles. Larvae were frequently found in direct
contact with mycelial mats of the fungus. Larvae of the two-lined
chestnut borer, _Agrilus bilineatus_, were most abundant, but larvae of
species of the families Scolytidae and Cerambycidae were also present in
large numbers.

In addition to the mycelial mat under the bark there was often present a
thick dark pad usually in the center of the mat. It is not known yet
what part this pad plays in the life history of the fungus but we do
know that it is produced by the same fungus which causes oak wilt.

We also found in Illinois that the oak wilt fungus often develops into
visible mats from chips of bark and wood that have been chopped from
wilt-killed trees and allowed to lie on the moist forest floor. This
should be remembered when considering sanitation as a partial means of
controlling the disease.

In 1951 the sexual or perfect form of the oak wilt fungus was produced
on laboratory media in Missouri by crossing different strains of the
fungus. The sexual form is recogn