id-71 WOODY PLANTS UNDER STRESS

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ID-71
WOODY PLANTS UNDER STRESS =
ISSUED:=20 7-88
REVISED:
Deborah B. Hill and William M. Fountain=20

When people see their woody = plants=20 (shrubs and trees) decline, they often want a "magical" treatment to = make them=20 lush, green and healthy again. But no magic exists. This publication = should help=20 you understand some common causes of woody plant stress, how stress = leads to=20 decline and what measures, if any, can make the tree healthy again. = Remember,=20 however, that all trees and shrubs like every living organism, will = eventually=20 die.=20

What Causes Woody Plant Stress?
All living organisms exist in a world of = stresses. Here we=20 are emphasizing unusual stresses that negatively affect normal health = and growth=20 of woody plants in a home landscape. Because plant problems arise from = physical,=20 chemical, biological and climatic factors, this publication defines = stress as=20 visible effects on your woody plants of one or more of these factors. = You may=20 see abnormal color or color changes, unusually small leaves, fewer = leaves than=20 normal, or a variety of other symptoms. (See also Cooperative Extension=20 Publication, ID-52, Environmental Stresses on = Woody=20 Ornamentals).=20

Plant Ecology and Physiology
First, let's review a woody plant's structure by = looking=20 at a tree. Each section of the tree performs unique functions but all = are=20 necessary for it to grow in a healthy manner.=20

Photosynthesis or = food-production takes=20 place in the crown. Foliage utilizes water and nutrients taken by = roots=20 and combines them with carbon dioxide from the air and energy from the = sun to=20 produce carbohydrates that fuel life processes of a tree. When something = interferes with normal photosynthesis, the tree produces less food for = ongoing=20 life and less reserves for the future. The time of year when = photosynthesis is=20 disturbed determines whether this year's or next year's growth is = affected.=20 Early season problems tend to affect the current year's growth, while = late=20 season problems tend to affect the next year's reserves.
The trunk (or bole) physically supports the = crown,=20 conducts nutrients and water up from the roots to the crown and conducts = food=20 down from the crown to the roots. Protected by bark, it serves as the = tree's=20 vital circulatory system. Inner bark is where new woody material is = formed each=20 year and also is where the transport system is located.
The roots support the plant, absorb water and = nutrients=20 from the soil for photosynthesis and "breathe." Their location is = important.=20 Because 90% of a tree's small feeder roots are in the top 6 inches of = soil, the=20 root system often extends outward from the trunk much farther than the = branches.=20 Many people mistakenly think that roots end at the dripline (the = farthest edge=20 of the branches), but they usually extend much farther. Therefore, = fertilizing=20 and other cultural practices should start within the dripline and extend = outward=20 at least half again as far as the distance from trunk to dripline.=20

Note: Since roots do = not observe=20 property lines, you may need to water and fertilize your neighbor's = property to=20 help one of your stressed plants.=20

Physical Stresses
The Wrong Place
Consider a plant's native environment. Species of = plants have=20 adapted to specific conditions over millions of years. Take the dogwood: = in its=20 native habitat it grows under forest trees or near the forest edge, = always in=20 partial or full shade. Leaves and stems die when the tree grows in full = sun,=20 because of heat and the wind's drying effects. Such constant stress may = also=20 make the tree more susceptible to insect and disease attack.
Any time you place a plant into an = environment where=20 it is not native, you are removing it from conditions where it has = thrived and=20 are placing it in a stressful situation. In a new location it may be = attacked by=20 new insects or diseases or it may affect or be affected by other plants. = Imported plants put in areas with soil types and/or climatic conditions = similar=20 to their native environment will probably have a better chance of = surviving than=20 ones not so well located. Follow these guidelines as you plant: =
=95Don't put plants into locations = that they=20 will outgrow. Be sure to ask how big your tree or shrub will be when = mature=20 before you buy it from a nursery. How far will its crown spread? How = tall will=20 it be? How big around will the trunk be? Because tree roots extend far = beyond=20 the spread of the crown, you should expect the root system to expand = twice as=20 far as the expected mature crown spread.
=95Avoid physical barriers such as building = foundations=20 and paved roadways. They inhibit the root system's expansion and = therefore=20 shorten a tree's life span.
=95Avoid=20 planting large woody plants in shallow soils with solid bedrock = underneath.=20 Such soils will force the root system to stay abnormally close to the = soil=20 surface where it may be more prone to drought and may require more = regular=20 watering during dry periods. This situation also makes trees more prone = to=20 windthrow.=20

Soil Compaction
Good = soil for=20 plant growth must be loose enough to provide spaces for air and water.=20 Compaction is compression of soil so that these spaces are reduced in = size and=20 number. Factors affecting soil looseness include:
=95Foot traffic from people and/or animals (either = livestock or=20 pets);
=95Vehicles; =
=95Paved driveways, sidewalks and roads, that limit the = effective=20 functioning of tree roots beneath them;
=95Construction, that often compacts soil with heavy = equipment;=20
Further construction problems include:
=95 Removing soil from the root zone, which causes = exposure and=20 root mortality;
=95 Adding = soil to the=20 root zone which causes overfilling and reduces the oxygen essential for = root=20 respiration (breathing). If fill is unavoidable, use tile drainage with = a tree=20 well. Consult a certified arborist or landscape contractor before = beginning=20 construction.=20

Pruning
Poor pruning = practices,=20 especially topping of trees, harm trees and shrubs. Aside from being = unsightly,=20 topping removes all normal leaf-bearing woody material and causes = heartrot.=20 Trees are weakened because they must take extra energy from their = reserves to=20 produce new foliage-bearing branches. Topping trees to avoid power lines = simply=20 aggravates the problem. Trees will form many fast-growing water sprouts = that=20 grow vertically and soon interfere again with the lines. Careful = directional=20 pruning, done by a trained arborist, encourages branches to grow = primarily away=20 from lines and can permanently solve the problem.
Not only is the method of pruning important but the = time of=20 year can also be critical to the plant's continued good health. Know = what=20 methods are appropriate for the woody plants you have. (For more = detailed=20 information see Cooperative Extension publications HO-59, Pruning = Landscape=20 Shrubs, and ID-55, Warning: Topping is = Hazardous to=20 Your Tree's Health.)
=95Some = deciduous=20 trees are best pruned during the dormant season (winter, early spring).=20
=95Certain flowering shrubs = and trees=20 should be pruned only after flowering.
=95Pines, spruces, maples, elms, beech, birches and = yellowwood=20 may "bleed" excessively if pruned in late winter or spring. =
=95Many shrubs and trees benefit from = shearing or=20 trimming during the growing season, but usually not in early spring when = buds=20 first break.=20

Bark and Wood Damage
Bark = and wood on=20 tree trunks are often inadvertently damaged by bicycles chained to = trees,=20 automobile collisions and carelessly operated lawn mowers or weed = trimmers.=20 Every nick on the bark provides a potential entry site for insects and = disease=20 organisms that are constantly present in the environment but normally = excluded=20 by the physical barrier of intact bark. Further, removal of bark not = only=20 interrupts circulatory activity at that point, but inhibits the tree's = ability=20 to make new woody material for that year. If the wound is not fatal = (e.g.=20 complete girdling of the tree) energy will go into its healing. = Interruption of=20 the two-way transport of carbohydrates, nutrients and water disrupts the = ability=20 of either crown or roots to perform effectively.=20

Chemical Stresses
Plants can also=20 be seriously damaged by toxic materials in the atmosphere or soil. Air=20 pollutants, such as sulfur and nitrous oxides from fossil fuel = combustion (e.g.=20 vehicles, power plants, industries) can cause localized problems such as = "burn"=20 on roadside plantings of trees or shrubs constantly exposed to vehicular = exhaust. Ozone, another atmospheric factor that occurs naturally at low = levels,=20 damages leaf tissue at high concentrations. Studies indicate that acid=20 deposition, whether as solid particles, fog, dew or other precipitation, = does=20 affect acidity of soil, but it is still unclear whether such = acidification is=20 enough to be harmful to roots or tree growth.
Salt applied to roads for snow or ice control can = infiltrate=20 soil around woody plant roots. Salt can change the soil pH and damage = roots, in=20 turn affecting leaves and branches dependent on those roots for water = and=20 nutrients. Spray that cars whip up off salted streets can float like fog = for up=20 to 100 yards, killing or damaging stems and buds on nearby dormant = plants.=20 Evergreens suffer even more severe damage from salt than broadleaved = trees=20 because they carry live foliage during winter months. Likewise, = excessive=20 application of fertilizer or injection of fertilizer into soil in = localized=20 spots can also kill roots they contact.=20

Biological Stresses
Some obvious=20 problems for woody plants are insects and diseases. Such stresses often = create=20 holes in leaf tissue, obvious discoloration, or distortion of leaf shape = in one=20 form or another. Defoliating insects, such as gypsy moth, are capable of = completely removing live foliage in spring and early summer. Often trees = and=20 shrubs can produce a second set of leaves after such defoliation, but = repeated=20 defoliations weaken plants considerably. Once weakened by such activity, = trees=20 and shrubs often become more susceptible to secondary invaders such as = boring=20 insects and canker fungi. (Several Cooperative Extension publications = are=20 available on insects and diseases of shrubs and trees. Contact your = county=20 Extension agents for details.)=20

Climatic Stresses
Weather = patterns=20 are never stable. Extremes in heat and cold or sudden temperature = changes have=20 occurred when, normally, a slow warming or cooling trend might have been = expected. Also, long periods when the soil has been excessively dry have = been=20 followed immediately by periods when the soil has been saturated. These = stresses=20 have killed many established plants and badly damaged others. =
The interaction of wide swings in = weather causes the=20 greatest plant damage. For example, in 1983 Kentucky experienced the = second=20 worst drought of the century and many trees and shrubs were forced into = dormancy=20 during the growing season. Fall brought rains and unseasonably warm=20 temperatures. Instead of beginning the normal process of hardening off = for=20 winter, many plants began putting on growth. When all-time record lows = were=20 experienced in December and January these plants were killed or severely = damaged. For example, southern magnolia (at the northernmost edge of its = natural=20 range in Kentucky) was severely damaged, in most cases losing its = evergreen=20 foliage and dying. Many trees and shrubs continued to show symptoms of = decline=20 in years following the 1983 drought. Long term effects of severe = climatic=20 conditions are not unusual in woody plants.
Periods of saturating rains in spring when trees and = shrubs=20 are beginning their new shoot and leaf growth are particularly damaging. = Water=20 excludes oxygen from soil and can result in "suffocation" and death of = the lower=20 root system. This lower root system is necessary for uptake of water and = nutrients during dry periods when feeder roots close to the soil surface = may dry=20 out and die. If drought damages feeder roots after saturating rains have = damaged=20 the deep root system, woody plants will suffer.
Too little water can be equally, if not more, = damaging.=20 Although you cannot remove excess water from the soil, you can water = trees and=20 shrubs during dry periods. One to 2 inches of water must enter the soil = each=20 week during spring, summer and early fall. If the 1-2 inches does not = occur as=20 natural precipitation, you must supplement it. A little sprinkle each = day (for=20 example, a tenth of an inch or less) will be more harmful than helpful = and=20 results in the formation of surface roots.=20

Spotting Symptoms
How can = you tell=20 your plants are declining from stress? Careful observation and common = sense are=20 the keys. Look for dead limbs, leaves that are off-color (pale green or=20 yellowish in summer), leaves drying out or margins (edges) of leaves = turning=20 brown, premature leaf drop, premature fall coloration in late summer, = holes in=20 leaves or skeletonized leaves (no green part, just veins), very short = areas of=20 new twig growth, and the presence of insects and/or diseases. =
You can be organized about your = observations.=20
=95Watch newly established = woody plants=20 carefully throughout the first two growing seasons.
=95Take pictures of valuable trees and shrubs annually = to help=20 you detect changes from year to year.
=95Ask for help from your county extension service. = Submit=20 samples (including branches, twigs and several leaves) through your = county=20 extension office when the problem first occurs.
=95If necessary, your county agent may consult the = Plant Disease=20 Diagnostic Lab or one of the Extension specialists in Horticulture or = Forestry=20 at the University of Kentucky. Careful and frequent observation is = important=20 because once the problem is easily visible, it has already become = serious, if=20 not irreversible.=20

Treatment
What can you do = once you=20 know that a plant is suffering from severe stress? The following list = includes=20 some very practical steps. If you do not yet have serious problems, = these=20 suggestions may be preventive medicine.=20

Avoid Drought Stress
If = your plants=20 have suffered from drought stress, make sure they do not suffer that = stress=20 again. Landscape plants should receive at least the equivalent of 1 =BD = inch of=20 rainfall per week during the growing season. If there are dry spells, = water with=20 hose or sprinkler until enough water has collected in a pan. If this = level of=20 watering causes runoff, three shorter periods of 1/2 inch of water each = time=20 during the day may be necessary. When watering, remember that tree roots = extend=20 well beyond the dripline. Use a soaker hose or some other slow-release = method of=20 watering, and move it around the tree area during the soaking period.=20
Mulching 2 or 3 inches deep = with some=20 organic material (compost, sawdust, woodchips, etc.) around newly = planted shrubs=20 and trees will help retain moisture for roots and provide protection to = the=20 trunk from lawn equipment.=20

Prune
Get the advice or = services of a=20 trained certified arborist or qualified landscape contractor for = corrective=20 pruning on your tree. You should remove dead limbs from the affected = tree=20 because of potential liability from falling branches, and selectively = remove=20 other limbs to improve the plant's form or health. Removing some live = material=20 will reduce the demand on the root system and allow the whole tree to = renew=20 itself. Never top the tree or remove more than a quarter of the live = crown.=20

Fertilization
When = deciduous plants=20 go into dormancy in the fall, apply fertilizer to improve their vigor = the=20 following growing season. If you already fertilize your lawn around = trees,=20 additional fertilization should not be necessary. Otherwise, you can = apply (at=20 normal lawn application rates) ammonium nitrate or a complete fertilizer = (e.g.=20 10-10-10) divided into equal parts two or three times during fall or = winter=20 (November to January). The ground should not be frozen and it should be = free of=20 snow cover when applying fertilizer. Most woody plants will show better = summer=20 and fall color, fuller growth and greater hardiness following this = treatment.=20 Fertilization can be repeated annually or biennially for as long as = rapid growth=20 is desired or the stress continues.
Some=20 plants may be too old or severely damaged to show positive results from = the=20 addition of fertilizer. Nitrogen added to trees under severe stress may = actually=20 increase the rate of decline. These severely stressed plants may put on = more top=20 growth than the root system is able to support resulting in depletion of = stored=20 carbohydrates. However, these severely stressed plants may recover on = their own=20 if watered and protected from other injurious factors. Making a decision = is a=20 judgment call in which you should consult a certified arborist or other = green=20 industry professional who has had extensive experience in saving = declining=20 trees.=20

Conclusion
Good = management of your=20 valuable woody plants may involve both "preventive" and "curative" = medicine.=20 Tips to remember for maintaining healthy plants in your home or farm = landscape=20 include:
=95Plant species = that are adapted=20 to Kentucky's climate and plant them in situations that mimic their = natural=20 environment.
=95Monitor = woody plants=20 during the growing season for signs of abnormal growth or general poor = health,=20 as well as for signs of harmful insects or diseases.
=95Be very careful with equipment such as mowers and = weed=20 trimmers so that you do not damage tree bark.
=95Keep trees and shrubs adequately watered during dry = periods.=20
=95Fertilize lightly during = late fall or=20 early winter to improve growth for the following year.
=95If you are unsure how to prune trees and shrubs = correctly,=20 have a trained arborist or landscape contractor do corrective pruning of = dead or=20 dying limbs.