"A natural forest typically begins as a large group of small trees, perhaps as many as several thousand to the acre. Over a period of many years, the numbers are reduced to only a few large trees per acre. Foresters, farmers and gardeners have long realized that an acre of land can produce only a certain amount of plant growth for either many small stems or for a few large ones."--First page.John P. Slusher (School of Forestry, Fisheries and Wildlife), Einar W. Palm (Department of Plant Pathology), Marc J. Linit (Department of Entomology), and Gary Long (Department of Horticulture)New 7/88/5

Linit, Marc J.

Long, Gary

Palm, Einar W.

Slusher, John P.

English

University of Missouri: MOspace

Tree Decline - What Is It? A natural forest typically begins as a large group of small trees, perhaps as many as several thousand to the acre. Over a period of many years the numbers are reduced to only a few large trees per acre. Foresters, farmers and gardeners have long realized that an acre of land can produce only a certain amount of plant growth for either many small sterns or for a few large ones. In general, the plants that survive are those that are best adapted to local growing conditions and those best able to effectively compete for sunlight, moisture and plant nutrients. There is a tendency for the strong plants to get stronger and the weak plants to get weaker, even-tually resulting in a natural thinning process. As the eventual losers decline in vigor, a few will pass out of the picture each year. Periods of drought, early and late frosts, wide fluctuations in temperature, insect and dis-ease epidemics, wildfire and other forces may speed up the natural selection process. As with humans, a decline in vigor causes more susceptibility to other problems. Insects and diseases, alone or in cornbina tion, may bring about tree decline and eventual death. In unmanaged forests natural forces decide which trees are to be re-moved. In managed forests, professional foresters make the decisions about which trees will be removed for the benefit of the forest. In this guide sheet we will discuss what takes place in the process of "tree decline" and how it is distin-guished from "tree death." The latter may be specifi-cally attributed to particular single causes such as oak wilt, Dutch elm disease or pine wilt disease. Whether a tree declines as part of the forest or as a shade tree in a yard, some of the same general principles and causes are often involved. Understanding the reasons for decline may help you prevent, reduce or sometimes reverse it for your yard or woodland trees. 5200 John P. Slusher, School of Forestry, Fisheries & Wildlife Einar W. Palm, Department of Plant Pathology Marc J. Unit, Department of Entomology Gary Long, Department of Horticulture Stress as a Cause of Tree Decline Various stresses are responsible for reduced tree vigor. These allow secondary diseases and insects to cause further decline and/ or death of branches, roots, or sometimes entire trees. One of the major causes of stress in trees is planting them in locations to which they are not suited. Some examples include: -Planting acid-loving trees in alkaline soils in-creases the likelihood of stress. -Planting "warm weather" trees in cold climates or moisture-loving trees in draughty soils almost always guarantees a life of stress. -Planting trees which require full sunlight for growth in the shade of other trees will also cause stress. A small pine tree planted in the shade of a stand of oak trees will never fully develop. -Planting trees which have the potential for large size in confined locations. For example, oak, pecan or other trees which develolp large tops and wide spread-Archive version -eck for updat sing root systems should never be planted in a 4-foot-by-4-foot hole in a sidewalk/ street location. Such trees are generally short lived under these conditions. -Planting trees which are intolerant of air pollut-ants where high levels of pollution are expected is not a good idea. For instance, trees such as white pine, larch, sugar maple, white ash and yellow poplar, which are sensitive to ozone should not be planted along freeways where automotive traffic is heavy. Instead, trees more tolerant of ozone such as eastern red cedar, black locust or burr oak should be considered. -Planting a tree which normally grows on dry up-land soils in low swampy areas is unwise. Wet area species such as pin oak, red maple, sycamore, sweetgum or bald cypress could be among the logical choices in such situations. Another major cause of stress in trees is allowing too many of them to occupy an area. Crowded trees com-pete with each other for nutrients, moisture and sun-light. As they increase in size there are not enough for all to survive. While some trees will eventually domi-nate, their growth is slowed and stress is created until the final survival decision is made by nature. There are many other factors which place trees in stressful situations and eventually lead to their decline: -Periodically, extreme conditions such as severe droughts or floods occur. Disease or insect epidemics may sometimes affect enough trees that people become aware and concerned about the situation. Heavy defo-liation can be caused by insects such as the variable oak leaf caterpillar, green striped maple worm, the elm leaf beetle and the gypsy moth. Repeated heavy defolia-tions seriously weaken trees and may well lead to prob-lems which can show up several years later. In the United States, oak species periodically have exhibited decline on a massive scale. In general, these situations have involved adverse weather factors combined with defoliation by insects or diseases. Finally, attacks on weakened trees by such things as root rot or trunk cankers or tree-boring insects result in serious decline and eventual death. -A similar situation often occurs on a smaller scale among shade trees following new residential construc-tion. Soil compaction by construction equipment, grade changes resulting in root damage from dirt removal, or root smothering by fill-dirt are among many factors that cause stress. Decline may not become evident for several years. -Compaction or other alteration of the soil over the roots will occur where the childrens' swing set or the family dog-pen is placed. Other residential yard activi-ties may further contribute to the problem. The slightly acid soil that oaks prefer may be altered by applying lime recommended for many turf grasses. -Alterations of natural drainage to move water swiftly away from the house may also reduce the mois-ture available to the shade trees. -Construction of driveways, sidewalks and streets can drastically modify the environment to which large shade trees have grown accustomed in early life. Many woodland trees are simply unable to survive the changes associated with their "urbanization." Many stress situations such as those listed can be avoided by checking with a tree-care professional or by acquiring a knowledge of the requirements of the tree species involved and the characteristics of the area on which the trees are located or will be planted. Symptoms of Decline Symptoms of decline may develop quickly or they may take years to become noticeable. Early symptoms include premature fall coloration, late spring leaf devel-opment, decreased twig and stem growth, leaf scorch, death of tissues between the leaf veins, and pre-mature leaf drop. Later symptoms include: dieback of larger limbs and branches; sprouting from the trunk of the tree; heavy seed crops; foliage noticeably smaller, lighter green and sometimes produced in "tufts" or "clumps" on sprout-origin tissues. The foliage over the entire tree may also appear thinner in decline conditions. There are certain fungi that cause stem canker or root infections that are often associated with the decline of many species of trees. When trees are under stress, physiological changes occur in the roots which allow the fungi to infect and kill them. In the autumn, clusters of honey-colored mushrooms may format the base of trees that have been infected. These growths indicate that root and trunk infections are present. Many wood- boring insects are also associated with the decline of trees. The ash borer, bronze birch borer and the flatheaded apple tree borer are some examples of insects that breed in various hardwood tree species which have been weakened by drought, defoliation or other adverse conditions. Scale insects are also com-monly associated with tree stress. Minimizing Stress and Tree Decline Tree decline can often be minimized by taking these preventive maintenance steps: -Avoid placing trees in a stressful situation. This includes selecting species of trees which are suited to the conditions of the planting location or modifying the planting site to suit the requirements of the species. -Do not try to grow more trees in an area than it will support. Woodland owners should consult professional foresters to determine how many trees of different va-rieties an area will support. Similar professional advice is available to homeowners about shade tree care. The local Extension center can assist you in getting this type of advice. -For planting in stressful situations select species that are the most tolerant of the existing type of stress. -Remove weak and dying trees to help prevent the buildup of secondary insectanddiseaseproblems. This practice can be carried out while making harvests for fuel wood or when thinning a group of trees. Decisions about which trees should be removed or left to grow should be made with some foresight. -In caring for trees in a yard, more intensive con-trol measures may be justified. Nutrient deficiencies can be corrected by proper fertilization. Properly timed watering will reduce moisture problems. Mulches to conserve moisture, prevent deep freezing and prevent soil crusting are usually beneficial. But do not apply mulches too deeply around stems. Insects or diseases may be controlled with spray programs using approved insecticides and fungicides according to label specifications. Dead parts may be pruned out, when warranted, to remove sources of dis-ease. Care should be given to avoid spreading disease on pruning tools by sterilizing the pruning tools with wood alcohol, household bleach or other approved disinfectants. Caution: do not mix bleach and ammonia products. Toxic fumes can result. Prevention of Tree Decline Here are some ways to prevent the common causes of tree decline: -Make sure new trees get off to a good start through proper methods of planting, fertilization, wa-tering and pruning. -A void wounding the tree with lawn mower, con-struction or logging equipment, children with axes, nails, brace wire girdling, etc. -Do not use harmful chemicals either directly on the tree or in the soil beneath it. Be careful with herbi-cides applied to the lawn. Always follow the directions printed on the label. Damage caused by the use of de-icing salt is a common problem. It is often over-looked because of the time that passes between salt applica-tions and the appearance of injury symptoms. -Do not top trees to shorten their height or change their shape. (See UM Guide 5160 for proper pruning procedures.) -Keep leaves, the tree's food manufacturing plant, healthy through appropriate fertilization and use of a spray program to control insect and disease problems. Fertilize by soil test or, if practical, by foliar analysis. Do not over fertilize or apply pesticides unnecessarily and always follow the directions printed on the label. -A void soil compaction of the root zone to main-tain proper moisture and air penetration to the root zone. -If you decide that a tree must be subjected to changes in soil grade seek professional advice on modi-fying the impacts. Your local Extension center will have publications on how to protect trees from grade changes or they can refer you to professional assistance. -Evergreen trees rarely survive a complete defolia-tion. However, most deciduous trees can tolerate one defoliation. A second defoliation in the same year or in two successive years may trigger a decline situation. Take extra precautions to avoid repeated defoliations. -It is helpful to know what kind of trees you have in your yard or woodlot. Most species have their own specific problems. Knowing the causes of tree decline and understanding how to keep your trees thrifty and healthy will help prevent early decline or premature death of your favorite trees. Your local University Extension center can help you find the information and sources of assistance you need. University ot Missouri ~~ 1839-1989 r\_')} University ~Extension UNIVERSITY OF MISSOURI LINCOLN UNIVERSITT' ■ Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914 in cooperation with the United States Department of Agriculture. Gail L. Imig, Director, Cooperative Extension Service, University of Missouri and Lincoln University, Columbia, Missouri 65211. ■ An equal opportunity institution. 5200 New 7/88/SM 

Tree decline - what is it?

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Tree decline - what is it?

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