Spotting The Root Of Tree Rot

September 15, 1990|By Amalie Adler Ascher

When their problems are pointed out to you, you begin seeing trees with new eyes. That's the way I feel, at any rate, after driving around one afternoon not long ago with William T. Rees at the wheel. Mr. Rees is a senior forester in the forestry management department at the Baltimore Gas & Electric Co. and a member of the Baltimore Country Forest Conservancy District. Noting that closing the space between his middle initial and his last name spells "trees," Mr. Rees feels he is "preordained to be in the business."

As manager of vegetation management at BG&E, a department that deals with trees around power lines, Mr. Rees is interested in educating the public. A tree in poor condition presents a safety hazard. The improper selection of trees gives rise to other complications. When a street tree exceeds a practical height, for example, it grows into utility lines and requires clipping, and that might detract from its appearance.

Indications that a tree is deteriorating are dieback at the top or a hole in the trunk.

These are signs that a tree may be rotting, perhaps clear to its base. It's hard to tell with certainty, Mr. Rees says, how far the rot extends. "A tree is a closed system and you can't look inside it."

It's not a good idea to bore into a tree to try to learn its interior condition. Making holes in a tree opens it to the entry of fungal infections and insects. While professionals do bore holes when they need to determine a tree's age and rate of growth, the practice should not be used to diagnose ailments.

When Mr. Rees sees a trunk with a cavernous hole in the trunk, he strongly suspects that the tree is not structurally sound and could easily be toppled.

Dieback at the top of a tree could also result from impairment to the roots. If the soil around a tree is sealed off or constantly walked on, roots will have less access to oxygen and moisture and may be subject to heat buildup. Trees selected for such sites should be types that can endure extreme conditions.

Heavy pruning is a last-ditch attempt often taken to save a tree or to buy time until a new one can be planted. Removing dead wood is also a safety measure. However, pruning live branches, especially large ones, is an art. It is best studied before undertaken or left to a professional. The branch collar (the ridge where the bark and wood tissues of the branch and trunk meet) should be left intact. Injuring or severing the branch collar destroys a major tree-defense system and also produces excessive sprouting. It's no longer recommended practice, by the way, to cover tree-cuts with pruning paint or wound dressings. A tree should be left to heal itself.

When a tree is losing bark, Mr. Rees says, it could be damage from improper removal of a branch, or it could be caused by lightning. Frost, too, can create cracks in bark. Because such wounds also provide access for insects and disease, any openings in the trunk suggest that insects or disease may already have taken hold and the tree may be in danger.

The appearance of sickly or yellowing foliage is more a symptom of nutrient deficiency than internal deterioration, Mr. Rees says. An imbalance in the soil may be reducing the tree's uptake of iron, or the tree might not be using the iron adequately.

Mr. Rees notes, as we peer at some, that sprouts or suckers at the base of a tree, or epicormic branches as they are technically called, usually indicate stress. Suckers can be removed, but the tree still has a problem.

Mechanical damage to the base of a tree can have severe consequences. A deep cut in a small tree, for instance caused by hitting it with a lawn mower, is as bad as a serious neck or head injury in humans, Mr. Rees says. Mulching around the base of a tree, but not so deeply that roots are suffocated, helps protect it against mower damage.

While it's natural for some trees' roots to entwine in a circular fashion, the condition can be fatal for other trees whose roots need more room to spread. Such girdling, as it's called, can occur when growing space has been restricted by, say, installing a curb, or through compaction of the soil, especially by heavy equipment on a construction site.

Fungus or conch growths, or what Mr. Rees calls fruiting bodies, on a live tree's trunk indicates a considerable amount of rot inside. Similar growths occurring at the base of a tree or on the ground around it are probably evidence of root rot. Such a tree, he says, "is a good candidate for removal."

For street-side planting, Mr. Rees advises choosing slower and lower-growing species or cultivars such as Kousa dogwood, serviceberry (alternately called shadblow), Japanese Tree Lilac or Sugar Tyme crabapple (a cultivar that doesn't drop its fruit.) Such ornamental trees enhance the landscape, although their shade value may not be great.

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