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Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915

7/29/02

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 August 2, 2002

Diagnosing Sick Trees

By
Paula Flynn
Extension Plant Pathologist
Iowa State University

Have you ever tried to seek shade from a tree with few, undersized leaves or one that barely seems to grow each year? Have you noticed a tree with scattered dead branches or a shelf-like fungus attached to the trunk?

If it's an important tree in your landscape, an initial reaction to these discoveries might be to quickly clip off a piece of one of the branches and take it to a garden center employee or tree care specialist for a diagnosis and remedy. You hope the remedy will be one that is fast acting. Maybe a pesticide or fertilizer will take care of the problem and restore lush green foliage to the tree.

Such a scenario rarely results in a fixed tree. An accurate diagnosis of a tree problem involves spending some time with the entire tree, looking closely for clues and replaying the conditions the tree has been exposed to in recent years. Trees, especially big trees, can take years to respond to a stressful condition. You may have to consider growing conditions from last year and even five or more years back in time to figure out the nature of a tree health problem. The owner of a tree is often the best person to provide insight into the primary cause of problem.

Figuring out the cause of a tree problem can seem a little overwhelming, especially if you're not even sure of the names of the trees in your yard. Take some time to find out what kind of trees you have and do research on what they need to stay healthy. You may be able to complete your diagnosis after this first step. For example, a shade-loving hemlock species may be growing poorly and slowly declining because it's been forced to grow in a hot, sunny location. The leaves of a pin oak might be bright yellow because the tree is planted in a site with a high pH soil.

Many times the problem is not in the leaves or branches, but in the roots, soil or the trunk. Important tree roots are in the upper inches of soil. These roots can extend out farther than the tree is high. Think about what could harm these roots.

Changing the slope around a tree by adding or taking away just a few inches of soil can lead to poor root health. Excessive watering can drown roots, and drought periods can be lead to scorching of leaves. New housing developments are often an enemy to established trees. Heavy construction equipment can compact soil, leaving roots to struggle to grow. Some tree species, such as oaks and hickories, are especially intolerant of construction activities. Tree roots can be injured by certain weedkillers, too.

Does pavement cover much of the root system? Do buildings surround the tree? Such trees often struggle when temperatures are high and moisture is scarce. Planting a big tree in a site with little room for the roots to grow is usually a recipe for a shortened life span for the tree.
After considering the many factors that affect root health, be sure to take a close look at the trunk of the tree. Is "mower blight" damage evident at the base of the tree? Do you see any splits or other damage that may have allowed the entry of decay fungi? Can you find any roots that may be girdling or encircling the base of the tree? Is it possible the tree may have been planted too deep? The bases of trees placed in the ground too deep tend to look like telephone poles, lacking the outward flare at the base of the trunk.

Be sure to consider our unpredictable weather in your problem diagnosis process. Trees going into winter suffering from severe drought stress are more likely to show problems the next season. This past spring, tender emerging leaf tissue was surprised by late spring frosts, causing damage that looked similar to an infectious disease.

There are a number of publications available from Iowa State University that will help you learn more about the proper care of trees and how to prevent problems. These publications are available from your local county ISU Extension office or from Extension Distribution Center at Iowa State University, Ames, IA 50011, (515) 294-5247.

Pm-1591 Community tree planting and care guide
SUL 2 Understanding decline in trees
SUL 3 Diagnosing tree problems

In many cases, more than one factor is contributing to the poor health of a tree. Insect infestations or infectious diseases may be involved. Complex problems may require assistance from a tree care professional or diagnostic lab. Help these specialists reach an accurate diagnosis by being prepared with plenty of information about the affected tree and nearby environment.

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