Many people ask the question, “What’s wrong with my tree?” The tree may have reduced growth and vigour, show physical injury, a change in foliage colour, have external resin or sap flow or have dieback. They will want to diagnose the problem or be able to describe the symptoms to a tree expert so that a remedy can be prescribed. Accurate diagnosis is often difficult in urban areas because the planted sites usually have been disturbed with introduced soils and surface compaction; have a disturbed drainage pattern and may have had various noxious material added (e.g. salts, herbicides etc.) that have contaminated the soils. These variables, combined with the effects of planting sites selected in relation to buildings, fences, cement walls and roadways, all impose changes and influences on tree root growth pattern and nutrient uptake.
Below grade influences are often difficult to predict, diagnose or identify because their affects are transferred through the root system. Above ground injuries caused by insects, diseases, air pollutants or climactic factors are more readily recognized. For most homeowners, a systematic approach to tree examination will help pinpoint problems or at least reduce the number of possible causes. Detailed observations and knowledge of recent soil treatments and weather records can be helpful.
Planting Related Problems
Survival of newly planted trees depends upon selection of healthy plant materials suited to the area, proper planting techniques and adequate post planting care. Newly planted trees may suffer transplant shock as they adjust to the new environment. Little new growth, some branch dieback or chlorotic (abnormally yellow) leaves may occur for 1-2 years until the root system becomes well established. Proper planting depth, good soil, a suitable location, seasonal timing and a regular watering schedule help to minimize transplant shock.
Infectious Damage Caused by Biotic Agents
A large number of native and introduced infectious fungal and bacterial diseases as well as insect pests attack trees in the Prairie Provinces. Many of these are easily recognized by the typical injury they cause, the tree species they attack, the life stage causing the injury and to some extent seasonal appearance. These biotic (living) agents may develop on weakened or infected trees and spread to adjacent trees.
Systematic infections caused by Dutch elm disease (a fungal parasite) and fire blight (a bacterium) initially cause wilt symptoms and browning of foliated branches and gradually progress to kill an entire tree. Dutch elm disease only infects elms, while fire blight infects mountain ash, crabapple, pear and other fruit trees. Silver leaf, a fungal disease of many fruit tree species can be diagnosed by the silvery sheen of the foliage and the presence of fungal fruiting structures on the lower stem. A group of rust fungi such as the pine stem rusts cause cankered infections on the stem or wood galls (western gall rust) on stems and branches. Another fungal disease Hypoxylon canker infects stems of trembling aspen, killing the trees after 4-6 years. Various other fungal pathogens attack the leaves and needles, causing a variety of symptoms on different tree species that include lesions, blotches and discolourations (spruce needle rust, pine needle casts and aspen leaf spot diseases).
Most insect defoliators feed in the larval or caterpillar stage and use leaves (forest tent caterpillar and cankerworms) or buds and needles (spruce budworms and yellow headed sawfly) as their food source. Sucking insects such as aphids may cause a yellowing of foliage, distorted, rolled or dicoloured leaves (wooly elm aphid) or pineapple-like galls (spruce gall aphid) on spruce twigs or secrete sticky honeydew. Faded, older needles with fine silk webbing on spruce and other conifers may suggest a high population of spider mites. Holes in the bark or stems of trees often associated with resin flow and sawdust indicates the presence bark beetles, wood borers or carpenter ants. Wilted or dying of the leader on a young spruce tree may denote attack by terminal weevils.
Examination & Diagnostic
When diagnosing the tree for various ailments or assessing its general health, people should examine all tree parts carefully from the root collar base to the buds and foliage, especially during the summer growth period. One should make note of any feeding or damage symptoms and associated insects or fungi; foliage discolouration and its location on the tree; branch or twig dieback; and recent growth pattern of buds, shoots and foliage. Once the examination is complete there are several good colour-illustrated books, brochures and tree pest leaflets available to assist the homeowner with identifying most of the common insect, disease or other damage causing agents in the Prairie Provinces. Injury that originates below ground may be difficult to diagnose but possible causal agents can often be identified. A confirmed diagnosis may, however, require additional analysis of soil, foliage or nutrients. If the problem cannot be adequately diagnosed by the homeowner, the symptoms on the tree should be accurately noted and samples of suspected causal agents and injury taken to a tree expert.
Cerezke, H.F. 1992. What’s wrong with my tree? For. Can., Northwest Reg., North. For. Cent., Edmonton, Alberta. For Leafl 23.