Nature Bulletin No. 479-A   February 3, 1973
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

****:OAK WILT

Our sturdy oaks, symbols of strength, toughness and durability, are 
menaced by a deadly fungous disease called Oak Wilt, They are being 
attacked in at least 18 states from Minnesota and Kansas to 
Pennsylvania and North Carolina. That is alarming to those who recall 
that, during the first 35 years of this century, all but a few of our native 
chestnuts were annihilated by Chestnut Blight -- a fungus brought here 
in young chestnuts from Asia. Since 1930, we have lost untold numbers 
of fine elms and are desperately battling to save the rest from 
destruction by Dutch elm disease caused by a European fungus. Now 
the oaks, most important of all our hardwoods, are similarly threatened.

Oak wilt was first described as a definite disease in 1942, and the 
fungus was identified in 1944. At that time it was unknown out side of a 
few locations in southern Wisconsin, northern Illinois and northern 
Iowa. It may have been present but unnoticed for many years. By 1950 
it was become widespread in those regions and had been discovered in 
Minnesota, Indiana, Ohio, central and southern Illinois, northern 
Missouri and, to the dismay of foresters and lumbermen, in the Ozark 
forests of southern Missouri. During 1948, two oaks in our Palos forest 
preserves were found dying from this disease. The next year there were 
72. Careful searches through the woods and from the air in helicopters 
have discovered greater numbers every year. The maximum was 212 in 
1954.

On red and black oaks the first symptom is a wilting and curling of the 
leaves -- usually near the top of the tree. They gradually become bronze 
or brown and drop off. The lower branches are affected last but the tree 
ordinarily loses all its leaves within a week or two and dies during that 
summer. There is no cure. None recovers. On white and bur oaks, twigs 
with wilting and dead leaves may be scattered throughout the crown 
while some branches remain outwardly healthy. Those leaves usually 
become light brown and may not fall off. The entire tree seldom wilts at 
once and, becoming more and more "stagheaded", may live several 
years.

Oak wilt spreads in at least two ways. One is overland -- in "jumps " of 
from a few hundred yards to a mile or more -- into previously healthy 
trees. Nobody knows how. The spores of the fungus may be carried by 
beetles or other insects, by tree-climbing animals such as squirrels, or 
by woodpeckers and similar birds. That vital question is being 
feverishly investigated.

The other way is underground from tree to tree. In a dense woodland, 
the interlacing roots frequently become grafted together where they 
cross one another -- especially those of the red and black oaks. 
Normally, such graft unions are beneficial but they become "pipelines" 
of infection when oak wilt strikes. In our forest preserves, before we cut 
down and burn every part of each infected tree, we dig a deep narrow 
trench around it and its neighbors: far enough out so that the fungus 
cannot be transmitted underground beyond that clump. It is the only 
control measure known, now.

In the vast forests extending southward and eastward from the Ozarks, 
oaks comprise about one-third and the most valuable of all hardwood 
saw-timber.

They support major industries using oak wood for lumber, flooring, 
heavy timbers, barrels, railroad ties and other purposes. In our Cook 
County Forest Preserves, in many state, county and municipal parks, in 
farmers' woodlots, around innumerable resorts and homes -- oaks are 
the principal trees. It would be a national calamity if we lose them.