Diagnosing Tree Root Problems
Diagnosing disease and insect problems can really be fun. The task
becomes more difficult when the problem is not something infectious
or related to insects. It takes time to wade through all of the site,
environmental and cultural factors involved and often this sort of information
is not provided. Here are some tips on diagnosing tree root problems.
There are, of course, many below ground reasons for the decline of
a tree. Drought, flooding, compaction of the root zone, poor soils,
planting too deeply, inadequate space for roots and many more factors
could be involved. Often, diagnosing such a problem involves a process
of elimination, ruling out possibilities that might cause similar symptoms.
One of the more difficult possibilities to eliminate is root rot. Most
gardeners believe that they cannot possibly know the health of a mature
tree's roots.
The first sign of any root problem is top decline. Look for a few clues
to determine whether a tree is growing well. You can see a tree's annual
growth by looking at the trunk cross-section. Most of us have done this
as children. We counted the number of rings to tell us how old a tree
was when it died. We have also looked at the thickness of these rings
to compare growth between years. A less destructive way to determine
the amount of growth is to look at the stems. Follow the stem tip back
to the first set of closely aligned rings (about 1/8 inch apart) around
the stem. That is one year's growth. Continue down the stem to the next
set of rings for the next year's growth. Continue down the stem to the
next set of rings for the next year's growth. Most trees grow anywhere
from 6 to 18 inches of twig length in one year. Of course, this varies
with the species and whether you are looking at a shady or sunny part
of the tree. If the tree has only grown one inch of twig for the last
two years and 8 inches three years ago, it is safe to say that the tree
is under stress and that the stress began two years ago. Cankers on
the stems, stem tip dieback, off-color foliage, early fall color and
early defoliation are also clues that a tree may be stressed by underground
causes.
To detect pathogenic wood rots and root rots, look for mushroom-like
fungi growing at the base of the tree or shrub. In the case of wood
rot fungi, the conks (also called shelf fungi or fruiting bodies) may
be found growing aerially on the trunk or main branches. These are signs
of the pathogen. The actual mycelia of the fungus is probably growing
in or on the roots or internally in the wood. One of the most common
examples is Gandoderma root rot, which produces a shelf type of fungal
structure at the base of many trees, especially honey locust. The structure
is reddish brown and appears to have been varnished. Its presence indicates
that a root rot has invaded. Other fungi may indicate wood rots. Wet
weather often triggers the formation of these structures. They could
easily be confused with fungi growing on dead organic debris near a
tree. If, however, they are growing from the tree itself, they are excellent
signs of wood rot or root rot.
You can also do some careful digging in the root zone of a tree to
try to determine the health of the roots. Do this near the drip line
at two or three spots. Healthy roots are brown on the outside but white
internally or at the very tips of the roots. If the roots have a soft,
brown outer layer that easily pulls off the center of the root, a root
rot may be involved.
Some experts say that the presence of conks on a tree or root rot in
the root system means that a tree will soon die. That may be the case,
but trees and shrubs may survive for many years with wood or root rots.
Do not remove a tree simply because it has a conk. Instead, use this
as a diagnostic tool in determining the true problem with the tree.
If the tree becomes a threat to life or property because of its potential
to fall or blow over, remove it as soon as possible.
No chemicals will help a tree in decline. Use approved cultural practices
to improve tree vitality, including weekly waterings of one to two inches
of water in periods of extended drought. Also, cut out dead branches
in the dormant season, fertilize in late fall or early spring and keep
traffic off the root system. For very old or very large trees, fertilization
and watering may have no benefit. On most trees, these measures may
help the tree continue to live for many years. Wood rot and decline
fungi do not have to be fatal.
Source: Nancy Pataky, Extension Specialist, Plant Clinic
Autumn
1999
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