The year 1997 has definitely been a tough year to be a
tree. From the time of spring bud break, through leaf expansion, and into the lazy days of
summer, many trees in the region spanning Indiana, northern Illinois, and southern
Wisconsin have unexpectedly collapsed and died. Others look very thin, with poor growth
and color. Still others are showing early fall color.
What’s going on? What is this mysterious malady affecting the
region’s trees? What about all these stories we hear about blights, anthracnose, oak
wilt, root rots, and the like? Is there anything we can do to alleviate these problems?
These are tough questions. Good answers are even tougher to come by. The
simplest reason for most of the tree failures we’ve seen can be summed up in one
word, “weather.” The hard part is figuring out which weather-related impacts
have affected a particular tree. It’s similar to being a physician examining a person
who has had a sudden heart attack. The doctor knows what the presenting symptoms are, but
may have difficulty in pinpointing why the attack occurred just then.
Many trees died this year as a result of a combination of weather effects
from previous years. For example, many white and red oaks failed to leaf out this spring.
The phenomenon seemed to be present throughout the Chicago region. Some yards were full of
25 to 40 inch diameter oaks that died over the winter. Investiga-tion of the roots often
indicated massive root rot infections. [Editor: Frank Mariani of Mariani Landscaping [Lake
Bluff, IL] told me that he had wondered how some dead oaks were even able to continue
standing, since their roots had virtually rotted away to nothing.] “Root rots”
are a fungal disease and require time to do their damage. As a rule, they usually leave
healthy trees alone and attack only trees under stress.
In most cases, we’ve been able to find a “trigger” that had
“set up” the tree(s) for problems. Many of the dead trees were located in areas
where the root systems sat in wet soils during the springs of 1995 and 1996. Remember how
much it rained during the springs of those years?
Consider the species of oak that have been affected. White and red oaks
were hit harder than bur oaks. We know that bur oaks are tougher trees. They withstand
construction injury and other root disturbances better than whites and reds, which in
nature are most often found on well-drained, upland soils. Take a white oak and put it in
a wet or damp soil, and we can expect problems. In nature, however, bur oaks are pioneers.
They are the trees which advance into grassy, moist, calcareous or other “tough”
sites from which other oaks will shy away.
“But wait”, you say, “These trees were mature. They’ve
been growing here for years.” True, but in many cases their environment has changed.
New subdivisions, roads, and other actions have changed the grade and drainage of land.
Areas that were once well drained or only held water for a short period now are forced to
contain water for much longer.
Saturated soils lead to root death. When combined with the 105 F summer of
1995 and the -27F winter of 1995/96, the root systems of many trees were overtaxed. With
their roots severely injured, trees had to use their stored energy reserves in 1996 to
survive. Root rots were able to get a foothold on the weakened trees. The root rot fungi
first work on the smaller roots, but if favorable conditions exist, the fungi will move up
the smaller roots into the tree’s buttress roots.
As the root systems begin to fail, the amount of water and nutrients
absorbed decrease. Lack of these raw materials cause a decline in the photosynthates in
the leaves. As the photosynthates decline, the root tissues that depend on them weaken.
The tree may then enter a “decline spiral” from which it may be impossible to
break free. They failed to leaf out in the spring of 1997.
Some of those trees that did leaf out in 1997, however, did so poorly.
Honeylocust, birch, and mulberry showed a great deal of branch dieback. Green ash was
affected by poor twig elongation, giving the trees a tufted, stunted appearance. Many of
the white oaks that did leaf out had yellow leaves: an additional sign of root/soil
troubles. The cool temperatures of May and early June contributed to above average levels
of foliar anthracnose diseases on oak, ash, sycamore, and elm.
Once the first blast of 95 F plus temperatures hit in late June and July,
we noticed sugar and Norway maples simply wilting and dying. Once again, dead roots,
girdling roots, root rots, and trunk cankers were obvious. The trees were able to survive
due to the moisture present during the cool spring, but then could not move enough water
from their damaged root systems to support their foliage during the hot weather. Crash!
The tree would wilt and dry up seemingly in front of our eyes.
Often, homeowners would say that the tree was fine until it suddenly died.
Closer scrutiny tells a different story, however. Looking at twig patterns over the past
few years, we could see the reduction in growth that indicated something was amiss. It is
difficult to prepare or correct for such extremes in environmental conditions. Trees
can’t move away from where they are growing. They must sit there and take what nature
(or humans) throw at them. A plant health care program that emphasizes proper watering,
mulching, pruning and fertilization is crucial, but it cannot guarantee success. As an
analogy, just because we exercise regularly, eat healthy, and do not smoke is no guarantee
that we will not succumb at an early age to cancer or heart disease. Our chances are
improved, but not guaranteed. Nonetheless, even a minimal tree maintenance program (such
as mulching) will go far in protecting homeowners’ investments in landscaping.
While this summer was one of relatively low stress, I shudder to think
what would have happened if we had been hit with drought. However, as I write this, it is
early September and many sugar and Norway maples are showing early fall color. They are
signalling that all is not well. Our trees are still teetering on the edge of the
“decline spiral”.
Sorting out pathological and environmental effects is difficult and
sometimes impossible. A professional who can properly diagnose a tree’s disease must
be a highly astute observer of both the natural and artificial environment in which a tree
lives. Unfortunately, what happened this year may be the result of conditions one, two,
even three years ago. Tomorrow’s tree health depends on the weather we receive today.
Hopefully, we will return to more average weather conditions in future years, and our
trees will have an easier life and chance of survival.
xxx
An entomologist by training, Rex Bastian is Director Of Technical Services
at Hendricksen, The Care of Trees, 2371 South Foster, Wheeling IL 60090. He may be reached
at (847) 394-8002 or at rexbastn@ix.netcom.com