Sunday, September 13, 2009

Bleeding Maples A Natural Condition?

By Thomas Fryd

Do shade trees have high blood pressure? Well, not exactly, but a high pressure does develop in the heart-wood of the trunks of some trees and fermented sap is forced out through wounds where branches have been cut off, through cracks in the trunk, or through a split at the crotch where two large branches unite. The liquid which is exuded is not the same as the sap which moves in the growing wood just beneath the bark. The "bleeding" of maple trees from wounds in early spring is a natural condition and is not the result of any disease.

Wetwood of Elms

For many years this flow of fermented sap from the heartwood has been called "slime flux," and its nature and cause were little understood. Slime flux, or "wetwood" of elm trees, as it has been called, is caused by a bacterial infection in the heartwood. The bacteria do not rot the heartwood, but cause fermentation which produces pressure sufficient to force the fermented liquid out through wounds in the tree. The sour-smelling liquid runs down, streaking the bark of the tree. Eel worms and insects are attracted to it, and molds and yeasts grow in it. The fermented liquid contains toxic materials which prevent the wounds from healing.

A great many elm trees have been affected by the wetwood disease. The flow of the liquid is usually greater in spring and early summer than during the hot, dry weather of July and August.

Elms affected with wetwood do not ordinarily die because of the disease, even though it may continue for many years, but apple trees and other trees are injured and the "running sore condition" is unsightly and annoying just like pruning apple trees. The grass is killed where the liquid drips. If the fermented liquid is forced into the sap stream, wilting and dying of the affected branches result. Dead branches frequently occur on trees that are persistent "heavy bleeders."

The occurrence of "hara-kiri" or committing suicide is fairly common among our parkway and shade trees. Occasionally a fine specimen of maple, elm or oak has taken its life by winding its own roots about the trunk, usually just below the surface of the soil and gradually, but surely, strangling its own life stream. In some cases a strangling root, cutting off the flow of sap on one side of a tree, will result in the gradual death of the top-most branches and those on the side of the tree where the damage is occurring. A tree so weakened becomes a host for borers which soon finish killing it. I have observed some fine specimen sugar maple trees whose basal trunks have been so constricted by strangling roots that the trees have broken off during a wind storm, there by disclosing the reason for the disaster.

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