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WOODY ORNAMENTALS: TREES, SHRUBS AND VINES |
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KEY CONCEPTS
II. Acquiring Woody Ornamentals
III. Planting Woody Ornamentals
IV. Maintaining Woody Ornamentals
V. Tree and Shrub Problems
Return to Introduction
TREE AND SHRUB PROBLEMS
Woody ornamentals may experience a variety of problems during their lives. Some of these problems are caused by disease organisms and insects. Other problems are brought on by old age. Additional problems are caused by weather stress, physical damage and human-induced stress.
Trees and shrubs have a natural life span. As a plant ages, the physiological processes of growth slow. The plant becomes less vigorous and more susceptible to disease and insect damage. The species, site conditions, weather conditions and maintenance influence how long a plant will live. It is important to realize that the large tree in the front yard will eventually die. Planning for the event as it nears will result in continuity in the landscape.
Most urban landscapes are planted in what is called disturbed soil. Topsoil may be removed. Soil from the excavation of basements ends up on the surface. The soil is compacted by heavy equipment. This results in poor soil texture and drainage with poor root growth potential.
A simple test for texture is provided in Chapter 2 on soils. To test drainage, dig several holes 1 foot deep and 1 foot by 1 foot wide. Fill these holes with water. If the water remains in the holes longer than one day, drainage should be improved by installing drainage tile, amending the soil by adding 1/4 to 1/3 by volume of organic matter, or installing raised beds.
Constructing planting mounds is an option where poor drainage is a problem. However, moisture still moves up into the mound by capillary action from the surrounding soil. Soil in a mound will dry out more quickly than surrounding soil. This will be a problem during droughts. Irrigation of mounds is tricky because the water tends to run off the sloped sides. Additionally, the roots of large trees will grow beyond the mound becoming surface root problems in surrounding areas.
Compacted soil lacks pore space. Pore space is needed for the exchange of gases through the roots. Increasing organic matter in the top foot of soil is necessary for trees and shrubs which have most of their roots in the top 12 inches of soil. Core aeration helps, but amending the soil before planting gives better results.
Adding soil over existing roots may result in a plant's death. This is due to reduced gas exchange and changes in drainage.
Weather and climatic stresses include high temperature combined with drought conditions and cold, windy conditions. Drought combined with high temperatures causes leaf scorch. The plants are forced into dormancy to cope with the conditions. A similar condition occurs when the soil freezes and plants are exposed to drying winds. Moisture is lost through the leaves of evergreen plants, desiccating the tissue.
Heat and moisture stress can result from roots covered with pavement. The paving limits moisture penetration of the soil and causes heat buildup. Street trees are subjected to this problem plus confined root area and road salt buildup during winter months. A soil test for soluble salts can potentially identify salt problems.
Pollution is an increasing problem in some areas. Acid rain and air pollutants can damage plant tissue. Although these are not as common as other stresses, they should not be overlooked.
The most physical damage is from lawn mowers and string trimmers. They can destroy the cambial tissue on the trunks of trees and shrubs. Mulching around trees and shrubs can help eliminate this problem.
However, mulching has also been abused. Mulch applied around the trunk of a tree or shrub creates the cool, moist environment advantageous for fungal growth. Keep mulch 3 to 6 inches from the base of the trunk. Mulching trees and shrubs to a depth of more than 3 inches of mulch reduces air exchange through the roots.
Construction damages roots by cutting them and compacting the soil over the roots. Roots of an established tree extend well beyond the drip line, yet protection during construction is often a fence a few feet from the trunk. A much larger area must be protected.
Most of a tree's roots are in the top 12 inches of soil; they can be easily damaged by spills of toxic chemicals such as petroleum products, herbicides and household cleaning products. Lawn care products that contain dicamba are used to control turfgrass weeds. Tree and shrub roots are susceptible to damage from dicamba. Weed killers containing dicamba should not be routinely applied over the roots of trees and shrubs.
Tree roots will grow in the path of least resistance. If they grow into a rock, the growth will be redirected. The potential for damage to sewer lines is minimal. Most roots are not that deep. Those that are will not break through a sewer line. Roots will grow into a sewer line only if cracks are already in it. Most roots do not grow where it is constantly wet.
Surface roots are a hazard. People can trip on them. Lawn mowers can damage them. Surface roots can damage pavement. Roots do not grow naturally on the surface. Young roots begin growing 4 to 12 inches below the surface. With age they increase in girth. Roots gradually become exposed. These roots should not be covered routinely with soil because this will change the drainage pattern and air and water penetration.
A better solution is to cover exposed roots with mulch. Plant a ground cover that will grow over the roots. Roots that are causing problems with pavement may be cut. To avoid continuing problems in the same or nearby areas, install root barriers. Root barriers (plastic, metal or herbicide impregnated fabric) can reduce problems with pavement and structures.
The question, "Will my tree die if I cut the roots?" often arises. There is no absolute answer. Any time the roots are cut, an entry path is created for diseases and insects. If work must be done and roots must be cut, making clean cuts with a sharp saw reduces the potential for infection or infestation.
The greater the number of major roots cut, the higher the potential for problems. Cutting more than 1/3 of the roots is not recommended because it disturbs the foliage-to-root ratio.
Trees that often develop surface roots include the following:
Acer platanoides : Norway maple
Acer saccharinum : Silver mapl
Fagus grandifolia : American beech
Larix decidua : European larch
Liquidambar styraciflua : Sweet gum
Metasequoia glyptostroboides : Dawn redwood
Morus alba : White mulberry
Picea pungens : Colorado spruce
Populus species: Poplars
Quercus palustris : Pin oak
Salix alba : White willow
Taxodium distichum : Bald cypress
Tilia species: Lindens
Master Gardeners must be aware of the different types of insect and disease problems that arise on woody ornamentals. There are many sources of information available to you. Each week during the growing season, agents from across Ohio and STATE SPECIALISTS participate in a conference call. Current problems are discussed and a summary of the discussion, called the Buckeye Yard and Garden Line, is sent out to all offices. Use this as a guide to current problems.
In addition to the fact sheet on particular insects and diseases, bulletins with current control measures are available for a small fee. Because chemical recommendations are constantly changing, the label on the pesticide must be read carefully. The label is a legal document and the instructions for use must be followed. Fines can be assessed for misuse. The plant to be treated must be on the label for a legal application.
A color brochure from the Ohio Nurserymen's Association having the most common disease and insect problems of landscape plants is Reference Woody.4.
Assistance with diagnosis is available through the Plant Pest and Disease Clinic on the Columbus campus of The Ohio State University. The current forms, instructions for use and fees are on file in Extension offices. You may use this service and you should encourage clients to use it.
Diagnosis is handled differently in each office. Check with the horticulture or agriculture agent for current procedures.
For problems on valuable trees, the service of a certified arborist is always recommended. Extension offices may have a list of local certified arborists; otherwise, listings can be found in the yellow pages of the telephone book under tree care.
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