Shade tree decline
A tree that just doesn't look quite as healthy as usual but does not have any specific disease or insect problem may be suffering from shade tree decline. Decline is a general term describing dieback of the branches in the crown associated with a general reduction of tree vigor. It can be caused by a variety of factors.
The symptoms usually develop slowly and may not be noticed immediately. The crown of the tree often thins out. New terminal growth may be limited and branches may die. Abnormally large seed crops are sometimes associated with decline, as is premature fall coloration and leaf drop. The leaves may become smaller and fewer in number. Trees affected by decline may survive indefinitely or may die within a few years.
Trees may decline for many reasons. Often times the symptoms can be confused with other specific insect, disease, or environmental problems making it difficult to diagnose shade tree decline.
The following is a list of factors that can contribute to tree decline. Often it involves physical injury from man, animals, machines, or nature such as:
- Repeated defoliation from insects or diseases.
- Adverse weather conditions such as cold or drought.
- Flooding or changes in the water table.
- Significant bark damage from lawn mower injury, frost cracks, or animal feeding.
- Soil fertility problems.
- Repeated injury from herbicides or other chemicals.
- Damage from construction around the tree due to soil fill, root pruning or soil compaction from heavy equipment.
- Accumulated salt injury from road salt.
- Girdled or restricted root development, often from planting too deeply.
- Graft union failure.
- Root and trunk rots as evidenced by mushrooms or other fungal structures.
- Environmental pollution.
In diagnosing shade tree decline it is important to remember that symptoms do not always occur immediately following the initial injury. Decline symptoms may not start until a year or two later.
The best way to control tree decline is to take preventive measures, whenever possible, to avoid the stress factors that contribute to the problem. If decline symptoms appear which cannot be traced to a specific insect or disease organism, try to increase the vigor of the tree by fertilizing in spring and providing additional water throughout the growing season. Prune out any dead wood or branches.
Following these steps does not guarantee that the tree will recover, but they may help the tree to survive for a longer time.