 Tree Health
Disease
Tree disease may be defined as a sustained and progressive impairment of the structure or function of any part of a living tree. It is ironic that one of the largest organisms on earth are killed by some of the smallest. Living agents are called pathogens. Few pathogens are able to successfully attack healthy plants. There are some aggressive pathogens that attack healthy trees, including sudden oak death, Dutch elm disease and chestnut blight.
Most pathogens, in order to be successful, need a susceptible host. The key to insuring tree longevity and performance is to eliminate stress-inducing agents from the tree’s environment. The three key advantages in preventing your trees from decline and disease susceptibility:
- proper tree selection for the site and space,
- proper soil management and
- appropriate pruning.
Pathogens
Tree pathogens can be broken into four principal groups:
Fungi are the most common plant disease agents.
- Fungi are filamentous, non-green plants that are widely distributed in plants, soil and air.
- The fruiting bodies they produce are called mushrooms, conks and molds.
- Though most fungi are beneficial, malevolent varieties are the most destructive pathogens, causing cankers, stem rot, root rot, wilts and various leaf diseases.
Bacterial agents are single-celled organisms that obtain food from organic matter.
- Bacterial infections on plants cause blights, crown galls and wet wood infections.
Viruses can only exist and reproduce in living cells and are parasitic.
- Viruses are seldom fatal, but they will dwarf or weaken the plant to the point where other pathogens will kill it.
- Most viruses are leaf or fruit based but some do attack stems and branch tips.
Mycoplasmas share traits with both viruses and bacteria.
- They are spread through insects (vectors) or through use of non-sterile pruning equipment.
- These nebulous agents often have the most devastating effect on their host, often by blocking movement of organic material in the tree’s vascular system.
- The two main diseases caused by these agents are lethal yellows in palms and witches brooms on many species.
- They are often fatal if not treated. Valuable plants can be treated with antibiotics annually as a preventative measure.
Tree diseases are commonly grouped based on the organ of the tree they attack:
- Foliage diseases
- Foliage disease over time will weaken the defense system of a tree due to decreased food production.
- In shade trees, leaf diseases decrease suitability of the plant for use in urban areas.
- These diseases include leaf spots, anthracnoses, blights, foliage rusts, needlecasts, mildew, mold and leaf blisters.
- Stem diseases
- Stem diseases weaken both the vascular system and the structure the tree needs to support itself.
- Chronic stem diseases are almost always fatal, usually by the time they are discovered, the tree is already in serious decline.
- Root diseases
- Root diseases are known as the silent killers because they are not easy to recognize by the untrained eye.
- Root diseases are most often found on trees that have been injured by construction or lawn equipment, planted in poorly-drained soils, or subjected to poor pruning practices in the past.
- Root diseases can cause poor performance, crown dieback and complete tree failure.
- It is vital that if you see mushrooms or other fruiting fungal bodies at the base or on the root systems of your trees, to contact a tree professional as soon as possible.
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