On oaks, particularly pin and red oaks, we could be experiencing
some major problems such as oak wilt and bacterial leaf scorch.
Other problems such as anthracnose (and other leaf spot fungi),
oak tatters and water damage are not to be overlooked, but they
usually don't signal the end of the tree is in sight.
has been a nonevent in our area, but the possibility does exist
that it will rear its ugly head. It is very similar to
verticillium wilt that we find in many of our shade trees and
has a streaking of the sapwood as a telltale sign. There is no
cure for oak wilt.
Bacterial leaf scorch is probably the main culprit in many
rapidly declining oaks. The bacteria cause the ends and margins
of the leaf to dry and turn brown. Some areas of the country
have reported temporary results from antibiotic injections into
the tree, but Midwest states have not reported any success.
Essentially there is no cure for BLS in oaks, with tree death
often coming within six or seven years of infection.
Amillaria root rot is another serious disease of oaks that
has become more prominent. This is caused by a fungus that
invades below ground. As is the case with many diseases, trees
that are stressed by flooding, drought or mechanical injury are
predisposed to getting the disease. Mushrooms at the base of the
tree or structures like shoestrings growing just under the bark
of the tree are symptoms of this disease. There is no real cure
for this disease at the present time either.
The leaf spot fungi problems are less important but may be
prevented with protective fungicides applied to leaves
throughout the spring and early summer. Figure on at least three
applications about 14 days apart at a minimum. It is also
important to get good coverage of all leaves. These diseases
weaken the tree by not allowing it to make as much food for the
year. Weakening for a year or two doesn't make much difference,
but over a long period of time we can get other problems on the
[to top of second column]
These same fungi are affecting most of our good-quality shade and
fruit trees. Anthracnose is the major fungus for shade trees; apple
scab is the culprit for apples and crab apples; and there are more
specific fungi that affect ash and other trees.
We'll have to live with what we have for this year, but a
preventive program may be in order in future years. We have actually
had outbreaks of the leaf spot fungus group each of the last 20
years. The little bit of weakening each year eventually catches up
For now the adage of "Keep trees in good growing condition" holds
true. Water with an inch of water per week when Mother Nature
doesn't provide it, and fertilize with a lawn rate (to provide a
pound of nitrogen, phosphorus and potassium per 1,000 square feet),
and that will go a long way in helping the tree overcome weakness.
University of Illinois Extension]