1) Girdling roots

Red, silver, sugar, and Norway maples often die as a result of a process that resembles self-strangulation. If trees are planted too deep or if the root systems are placed in a hole that is too small, some roots may eventually wrap around part of the stem. The consequences of this misfortune may not be noticed for many yeas, but eventually the stem and offending roots reach sufficient size to restrict growth of each other. With continued growth of stem against root and vice versa, cellular organization of stem wood is distorted, diameter growth of the stem slows, and the affected tree or parts thereof die.

Diagnosis of girdling root injury can only be done by locating one or more girdling roots. Sometimes, these can be seen at the soil surface, but more often they must be excavated. It is not unusual to dig down 50 cm to locate such roots.

The best way to deal with girdling roots is to prevent their occurrence. When planting maples, be sure that the root collar is at ground level; do not plant too deeply. In addition, be sure that planting holes are at least 1 1/2-2 times as wide as the root mass, and take time to spread the roots out before backfilling. Prune any major roots that are not growing away from the main stem.

On older, established trees with girdling roots, there is no option but to sever the offending root(s). However, remember that even though a root is girdling one part of a stem, the same root is also nourishing another part. Thus, any removal of major roots must be accompanied by a rigorous program of watering and fertilizing.

2) Iron or manganese chlorosis

Red, sugar, and silver maples on neutral or alkaline soils usually have foliage that appears to be "off color." Upon close examination, typical symptoms of iron or manganese deficiency usually can be seen; cells near leaf veins are green, but the rest of the leaf is yellow.

The problem can be prevented by checking soil pH at a planting site before selecting a tree for that site. Then, choose a species that can tolerate existing conditions.

If established trees start to show iron or manganese deficiency after yeas of good health, that is usually because the roots have grown near limestone bedrock. The only remedy is to supply needed nutrients through supplemental fertilization. However, it is very important to have foliage chemically analyzed before fertilizing. Otherwise, a nutrient that is not in short supply may be added, and injury from overdose could occur.

3) Deicing salt injury

Roadside maples in northern climates are inevitably exposed to massive doses of deicing salt. Red and sugar maples are extremely sensitive to salt, and thousands have died as a result. Salt tolerance of box elder and silver maples is moderate, and Norway maple is quite resistant.

Symptoms of salt injury are seen most often in leaves as general yellowing and marginal scorch. Repeated exposure causes death of twigs and general decline that may lead to death of entire trees. When choosing trees for roadside planting, do not use maples or other trees with low salt tolerance.

(See Bulletin 169—Salt Injury to Roadside Plants, published by the Cornell Cooperative Extension, for further information.)

4) Freezing injury

Rapid freezing and thawing often causes wood to crack around previously contained defects in stems of maples. This is particularly common on trees growing in open sites as in nurseries, but it may occur in forests as well. Once a frost crack does occur, it may open and close as temperatures fluctuate in future winters, and a rib of callus (a "frost rib") will form along the cracks. These cracks are common sites for wood decay and they should be evaluated by a professional arborist above photo.

Maple leaves also may be injured by freezing temperatures because they are formed in buds one growing season be fore they emerge. Freezing and thawing of buds may injure parts of these pre formed leaves, and when they finally expand in spring, the leaves have holes in them. Freezing injury to leaves can be distinguished from holes caused by other agents in that holes due to freezing usually occur in pairs and are often equidistant from a major vein of the leaf.

Because maple leaves emerge earlier than many other species, they are often killed by late spring frost. Results of such frosts may leave whole forests looking ragged and bare, but the injured leaves are soon replaced by new ones.

5) Maple decline

The foregoing discussion of infectious diseases and cultural maladies illustrates the wide variety of problems that threaten maple tree health. In addition, more than 70 insects feed on maples. Often, several diseases, insects, and/or environmental conditions combine to kill maples slowly or in what appears to be swift and dramatic fashion. (See Armillaria root disease section as an example.) As no single agent is solely responsible for such demise, the diagnostician must piece together a complex series of events and refers to the end result as "maple decline." Unfortunately, by the time that most maple decline is finally noticed, the tree in question is beyond salvation. Judicious pruning, watering, and fertilizing may help to prolong the lives of declining trees, but it is virtually impossible to restore them to their original splendor.