From the Pests of Ornamental Series
Homeowners are Frequently problemed by the fact that ......"The leaves on my trees are turning brown" or "Some of the branches are dying" or "My whole tree is beginning to look sickly."
Unless the Extension Service specialist in the pest identification laboratory can see specimens of the dead or diseased plant, it is usually impossible to even guess what is wrong. Even then, it may be difficult to determine the cause of the problem after examining the dead leaves, twigs, branches, or roots that are enclosed with homeowner inquiries.
If leaves have spots caused by fungi, bacteria or viruses, the trouble can be identified and recommendations given. But, often the leaves are dead or dying merely from lack of water due to a disease or disturbance elsewhere in the tree. These leaves give little or no clue to the direct cause of death. Often the fungi present on specimens are not the direct cause and start to grow after the twig or branch dies.
In many cases the answer to a tree problem can be determined only after a careful inspection of the tree and its surroundings. Here are some clues that may help in solving a tree problem.
When a tree is transplanted, it usually passes through a period of shock. Nature provides a balance between the root system and leaf crown. If the tree came from.a reputable nursery, the roots were probably pruned for several years to form a compact ball of roots that could be taken up with the tree. Such pruning avoids undue disturbance of this natural balance. But, if a tree is dug from the woods or field, where no previous root pruning has been done, its chances of survival are not too good. If this is done, cut out at least one-third of the branches, at transplanting time. By doing this, the number of leaves that will grow during the following season will be reduced, which will increase the chances for survival.
This "blight" is common in recent development areas where wooded sections of land have been cleared and homes have been built among the remaining trees. The trunk may be so badly damaged that little bark remains. Other trees may have been protected so that earth-moving equipment did not damage the trunk; however , the heavy machinery compacted the soil and injured the roots.
Beech trees almost invariably die in home development areas, regardless of the care given them. Dogwood, sweetgum, and some oaks may die, also.
Changing the grade under a tree means adding or removing soil in the area of the root system. The removal of even a few inches of soil will take with it some of the feeder roots and cause shock to the tree. The injury produced by lowering the grade is negligible, however, compared with that caused by adding soil to raise the grade. An improperly applied fill of as little as 6 inches can seriously affect some trees. If the area has not been prepared properly, the application of a fill of a foot or more will kill many trees. Building a wall or leaving a,well,around the base of a tree is of little or no value.
Trees growing in poor locations may have a hard time getting enough water to supply their needs even in normal years. During an extreme drought, the moisture in the soil may be so reduced that many of the feeding roots will die. Leaf scorch may result during even a short period of dry weather.
Excessive Moisture or Poor Drainage
In areas where the subsoil is a heavy clay, a recently transplanted tree may die, because of excessive water in the soil. Filling the planting hole with good sandy loam or peat does not change the water problem. If excess water cannot drain out of the planting hole, the newly planted tree may not have too good a chance for survival.
Dig a hole where the tree is expected to be planted and pour in several buckets of water. If much water is still there the next day, then expect trouble with a tree planted there. In these areas, plant the tree "high" in the hole rather than setting it too deep. It may be well to put drainage tile in the bottom of the hole to drain off the excess water.
Trees Surrounded By Pavements or Buildings
Trees growing with a street on one side and a sidewalk on the other are usually the first to show the results of drought or high temperatures.
Allowing water to run slowly from a hose in any open soil under the crown spread will often do much to help the tree. A partial thinning of the top of the tree will help balance the root and leaf ratio and allow the rain to penetrate the crown to:the soil around the trunk rather than cascading from leaf to leaf so that most of it ultimately falls on the street or on the pavement.
When planting a tree, in many cases the hole is dug too small to accommodate the outspread roots. Also, the roots may be wound around the base of the tree so that all fit into the undersized hole. Meanwhile, the trunk grows in diameter until the roots are in direct contact with it. A few years later, the roots, which are now even larger,will be cutting into the tree and choking it much as would a rope around the neck of a man. Such "girdling roots" can cause untold damage to growing shade trees.
The first symptom of a girdling root is the gradual decline of a branch or branches on perhaps just one side of the crown. Every year, more and more branches will die, until finally one whole side of the tree may be dead. Before this stage is reached, an examination of the trunk at the soil line will reveal the presence of girdling roots, regardless of whether they are at or below the surface of the soil. Most trees, even while still relatively young, will show a slight to moderate buttressing of the trunk at the soil line. If the crown is not too far gone, cut the troublesome root or roots from the trunk with a sharp chisel.
With the increase of container-grown stock in recent years, many trees start out with the root system badly disfigured. Roots of seedlings in pots, cans, or plastic containers quickly reach the confines of the container and then start to encircle the soil ball. In later years, the small encircled roots enlarge and result in the strangulation of the young trees.
There may be a gas leak 100 or more feet up or down the street from a tree that has died, although smaller plants, shrubs or even trees closer to the leak are apparently uninjured. This is due to a very hard and compact layer of soil, "hardpan," that may prevent the gas from. escaping to the surface at the point where the gas line break occurred, and the gas may seep horizontally for a considerable distance through the ground beneath the hardpan. Investigate all possibilities. If insect, disease, drought, or root injury is not the problem, then. and not until then, ask your public utility company to investigate for a possible gas leak in the vicinity.
Approximate time of death of a tree may be associated with a loud crash of thunder. Although a stroke of lightning that kills a tree will usually leave loose bark hanging from the top toward the ground, a tree may show no outward signs of the stroke. Some trees may be killed completely. On others, a few of the topmost branches will be killed. On some trees, when the trunk has been killed from top to bottom, not only will the leaves remain green through the season, but the tree will leaf out again the next spring. If the bark around the circumference of the trunk has been killed, it can live for no more than a year or two.
Septic Tank Injury
Strong chemical agents used in the household disposal system may escape from the septic tank into the surrounding soil and cause injury to trees. Occasionally, leaks or breaks in septic tank grease traps buried in lawn areas, will injure tree roots. Large quantities of Borax used in laundering and released through the drain field for septic tanks may appear on only one side of the tree - usually on the side nearest the tank.
Some spray materials that are noninjurious to certain species of trees, for instance, are extremely toxic to other species, or perhaps the concentration used on one type of tree is not adapted to another. Some sprays should be used only in very early spring, when the tree is leafless; if they are used on new green foliage, the results may be disastrous.
During certain years, a normally noninjurious spray may cause leaf burning on trees. When the spring is exceptionally wet and cloudy, leaves are exceptionally tender and in some instances, are spotted and burned by otherwise "safe" spray mixtures.
Only one or several trees in a large group of the same species may be injured by a spray. This usually results when the injured trees were slightly off balance as a result of previous drought injury or some deep-seated disease in the heart or roots that could not be detected.
Herbicide or Weedkiller Injury
Weedkiller injury could be suspected if leaves are shaped, twisted, cupped and unusually small with light-colored veins in contrast to the darker green interveinal portions. Some weedkillers are hormone materials that may cause the exotic leaf formations. A weedkiller, applied to one comer of a yard or several blocks to a half mile away, may drift into a tree on a windy day and result in damage. At other times, these chemicals may be used in excess or too close to a tree, in which case, the tree roots may take up some of the chemical and leaf injury may result.
Do not use a weedkiller in your spray pump and later apply fungicides or insecticides with the same sprayer. Injury is almost certain to result.
Do not apply weedkillers or herbicides under trees, near shrubs, or hedges.
Air Pollution Damage
Air pollution from industry, automobile exhausts, fires of all types, and fumes given off by some chemical processes has resulted in damage to trees and plants. In some cases, the exact pollutant can be identified by merely recognizing the characteristic injury symptoms it produces on some plants. In other cases, a pollutant may be suspected after observing the localized area in which plants are damaged.
In many cases, not all specimens of the same tree species will exhibit injury symptoms. This is due to the heredity or parentage of the tree. One white pine tree may be yellow and stunted, while the one next to it is dark green and growing rapidly.
Other Causes For Sick Trees