Almost all species of woody plants are subject to trunk and limb decay. Wood decay is one of the most important tree problems in the urban landscape. The progressive deterioration of woody tissue in both living and dead trees can occur in a relatively short time (months) or can grow slowly, taking years. Decay is good in a natural forest as it is essential in the recycling of organic components of plant tissues. However, decay in a living tree next to your house or garage, in a park, along a street, or in another high hazard area is not good. The combination of the sheer weight of the wood and the chemical and physical properties of decayed wood can result in tree and/or limb failure.
Symptoms
A good indicator of decay is the presence of fungal fruiting structures on the trunk, limbs, or roots. Fungal fruiting structures come in a variety of shapes such as bracket, shelf, hoof (collectively called conks) and mushroom (toadstool). Textures can range from spongy, stringy, crumbly, flaky, woody, leathery, corky, to fleshy. Color may be yellow, orange, brown, white, or black. Sunken or raised areas that are wet or dry on trunks and limbs can also be indicators of decay. Open wounds at the base of a tree or spots where limbs have failed or have been pruned (especially improperly pruned) often signal extensive wood decay.
On the other hand, identifying trees with wood decay can be difficult at times. Decay that occurs cylindrically in the center of the trunk may be hidden from view by a ring of healthy wood and bark. There may be no external evidence of advanced decay. Trees that show a gradual decline in vitality with twigs and then branches dying back may be extensively invaded with wood-rotting fungi.
Cause/Conditions
Wood rot diseases are caused by a wide variety of wound-colonizing fungi and occasionally by bacteria. Infection almost always occurs through moist, unprotected breaks in the bark where the wood underneath is exposed. A tree is wounded many times during its life. These wounds include summer or winter sunscald, fire scars, lightning strikes, frost or drought cracks, damaged roots, insect wounds, sapsucker punctures, breaks due to ice, snow, or wind, pruning cuts and branch stubs, mowing bruises, cuts made by knives, bicycles, automobiles, snowplows or construction equipment. The colonizing agent is brought to the tree by air currents, rain droplets, the wounding agent, insects, birds, or other animals.
Decay fungi destroy the tree’s internal supportive and structural components (cellulose, hemicellulose, and sometimes lignin). Decay fungi are often placed into three groups; white rots, brown rots, and soft rots. White rots break down lignin and cellulose causing rotted wood to feel moist, soft, spongy, or stringy and to appear white or yellow. Brown rots decay primarily the carbohydrates (cellulose), leaving behind the brownish wood lignin. Affected wood is usually dry and fragile and crumbles readily. Brown rot is usually more serious than white rot as it generally forms a column of rot in the trunk. Soft rots can be caused by either bacteria or fungi. They decay areas only directly adjacent to their growth and they grow more slowly, generally not causing extensive structural damage to living trees.
Management
By the time it becomes obvious that a tree has wood rot and decay, it is very difficult to manage. A number of factors can reduce the risk of serious damage. Give proper cultural care to keep plants vigorous. Water during periods of drought, fertilize annually, and mulch properly. Protect trees from injuries. Properly prune young trees to promote good structure and avoid the need for large limb removal in older trees.
Trees growing in significant “Target Areas” that exhibit any of the symptoms of Rot & Decay need to be checked by an experienced Professional Certified Arborist for Tree Failure Risk.
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