Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
8/4/03
Contacts:
Paula Flynn, Plant Pathology, (515) 294-0581, pflynn@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning Aug. 11, 2003
Examining the Causes of Troubled Trees
By Paula Flynn
Extension Plant Pathology
Iowa State University
"What is wrong with my tree? The leaves are dying and dropping.
Whatever is wrong with the tree is spreading fast. Is there anything I
can do to save the tree?"
Question likes these pour into Iowa State University (ISU) Extension county
offices every spring and summer. Trees are often subjected to a barrage
of stresses. Sorting through the possibilities is challenging, but it
is essential to try to help troubled trees. What do they need to be saved
from: drought, a fungus, a careless mower, insects, low temperatures,
herbicides or compacted soil?
Concerned tree owners typically hope that an examination of the leaves, branches and trunk may reveal the culprit and allow for a successful treatment recommendation. Although this sort of instant diagnosis is sometimes possible, the causes of tree problems are often more obscure.
The tree's root system, well hidden beneath neatly manicured lawns, flower beds or parking lot concrete, is too often forgotten in the diagnostic process. Frequently, however, poor health of the root system is the source of the gradual decline of the trees in our landscapes.
What do tree roots need to stay healthy? Most importantly, they need water, air and minerals from the soil. Some tree species can do remarkably well in tough urban conditions, while others do not. The correct diagnosis for many tree decline situations is that the wrong tree species was originally selected for the site. So it pays to do some homework before planting trees. Nobody wants to spend money on a tree and labor to plant it, only to watch it struggle and fail to thrive.
A recent field trip to northeast Iowa brought together foresters, entomologists, plant pathologists and tree care specialists to investigate the decline of urban trees, especially maples. In addition to taking a close look at the surrounding site conditions and the parts of the tree above the ground, root collar excavations were performed. The root collar is the area where the trunk connects to the roots.
From a distance, the trunks of most of the sick maples we examined looked like telephone poles. In other words, trunks lacked a gradual outward flare at the base, which is usually a good indication that a tree was planted too deep.
Root collar excavations revealed that one tree was planted 12 inches too deep and another was planted 18 inches too deep. The trees responded to the improper plantings by sending out roots closer to the soil surface. Unfortunately, these roots, also known as adventitious roots, grew around the trunk rather than outward. Over time, these roots encircled the trunk, slowly cutting off the uptake of water, oxygen and nutrients from the soil. To avoid this problem when planting a tree, dig the hole only as deep as the root system, and be sure the uppermost roots are at the level of the soil surface or slightly above.
Another sick maple was surrounded by a raised planting bed filled with flowering annuals and perennials. Landscaping blocks had been placed around the tree and several inches of soil had been added. Frequent watering of such plantings, the addition of soil and disturbance of the root system can lead to poor root health. These practices deprive tree roots of oxygen and damage root tissue. In addition, wet soil against the trunk can encourage decay.
Excavating a third maple revealed the presence of a non-degradable plastic wrap around the root ball of the tree. The wrap had never been loosened from the base of the trunk and was strangling the tree as the trunk expanded outward.
Finally, several declining maples examined showed physical damage from mowers at the base of the tree. Wounds created by careless mowing allows entry points for wood decay fungi, which can gradually rob trees of their vigor and may even make them unstable.
When trees are stressed by poor site conditions, improper care or environmental stresses, they are often more susceptible to insect and disease problems. Wood-boring insects, for example, are often attracted to declining trees. Canker fungi are also much more active on trees that are under stress.
Understanding the needs of trees, using proper planting techniques, and continually caring for them is the best way to keep trees healthy and avoid problems with decline. Thorough and proper diagnosis provides the best chance of successful management when a problem occurs.
For more details on diagnosing and managing declining trees, consult these ISU Extension publications:
Understanding Decline in Trees (SUL 2)
Diagnosing Tree Problems (SUL 3)
Planting Landscape Trees (PM 422)
Community Tree Planting and Care Guide (PM 1591)
Using Mulches in Managed Landscapes (SUL 12)
The publications give advice on proper planting and care techniques may be ordered from your local ISU Extension county office or from the ISU Extension Distribution Center by calling 515-247-5247.
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Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The fullsize photo is 480K. Caption: Sparse foliage on this tree may be caused by poor site conditions, improper care or environmental stresses. |
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