"Decline" is a general term describing the gradual reduction
of growth and vigor in a plant. "Dieback" refers to the progressive
death of twigs and branches which generally starts at the tips (Figure
1). Trees and shrubs affected by the decline and dieback syndrome may
die within a year or two after symptoms first appear or in some cases
survive indefinitely. Corrective practices such as proper watering, fertilization,
and pruning are not guaranteed solutions in all cases.
Decline and dieback may be caused by many factors (Figures 2 and 3) and
is usually progressive over several years. Trees and shrubs of all ages
may be affected, although this disease complex is usually associated with
plants that have attained some size and maturity.
Symptoms of decline and dieback are often subtle, slow in developing,
and usually uniform throughout the crown. A tree or shrub in the
dieback stage, however, may have localized symptoms such as apparently
healthy twigs and branches adjacent to dead or dying twigs and branches.
Dieback usually begins in the top of a plant and progresses downward,
but it may start on the lower branches, especially with conifers.
General symptoms of decline and dieback may include pale green
or yellow leaves, delayed spring flush of growth, scorching of the
leaf margins, small leaves, reduced twig and stem growth, early
leaf drop, premature fall coloration, and, as the disease complex
worsens, thinning of foliage in the crown, dieback of twigs and
branches, and production of suckers on the branches and trunk (Figure
Leaf scorch, a yellow to brown discoloration of the leaf margins
and tip, is commonly a part of the decline and dieback syndrome,
however, lack of adequate soil moisture, resulting in less water
reaching the leaf tips and margins can also cause scorch. Abnormally
large seed crops, sometimes associated with decline, is a normal
response to certain weather conditions. In some tree species, heavy
seed production occurs normally every few years.
Premature fall coloration, delayed spring flush, decrease in twig
growth, and early leaf drop are typical symptoms of maple, oak,
ash, honeylocust, birch and sweetgum decline and dieback, and the
conditions usually become progressively worse each year with the
leaves becoming smaller in size and fewer in number.
1. Dieback of maple caused by chemical injury.
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2. Site factors that can lead to tree decline and dieback (Purdue
Trees and shrubs are long-lived and over a period of years are
subject to attack by a variety of insects and diseases (Figure 3),
extremely high or low temperaturesespecially harmful is a
rapid drop in temperature following a period of mild weather in
the fall or spring(Figure 4), great fluctuations in soil moisture
during long-term weather cycles, mechanical damage to roots from
construction (Figure 5) or livestock, and numerous other environmental
effects (Figure 2).
These stress factors alone or in various combinations can reduce
leaf and shoot growth (that is, initiate decline) and lead to dieback,
although decline and dieback rarely result from a single stress
factor. The combination of human impact on the local environment
and natural climatic changes provides a multiplying effect that
is more serious than any single factor. Usually a tree or shrub
is first injured or damaged by disease (Figure 3), insect attack,
or adverse soil or air environmental conditions (Figure 2). The
damaged or weakened plant is then subject to attack by one or more
secondary organisms or agents. For example, trees and shrubs weakened
by drought or neglect are more susceptible to attack by borer-type
insects and canker diseases than healthy, vigorous plants. Severe
defoliation by leaf-eating insects, diseases, herbicides, hail,
or wind at critical times of plant development also may initiate
decline and dieback. If a defoliated plant develops new leaves late
in the year, and if these leaves are, in turn, killed by an early
frost, the plant will be low in food reserves and more subject to
winter injury. Weakened trees also are subject to invasion by various
fungi. Armillaria root rot, for example, commonly attacks and kills
the roots of weakened trees. Many other fungi attack the lower trunk
and buttress roots of weakened trees.
Of the many stress factors that can initiate the beginning of decline
and dieback, those that weaken or damage the root system are perhaps
the most threatening. In most instances of decline and dieback the
deterioration of the root system or the blockage of normal root
functions occurs before any symptoms are visible in the crown. The
root system is especially vulnerable to changes in the soil environment.
Soil compaction, changes in the soil drainage pattern, excessive
soil moisture (from rain or poor drainage) or lack of water (from
prolonged drought), the removal or addition of soil over the root
system (Figures 1 and 5), soil compaction, and chemical injury from
excess deicing salt, pesticide (Figure 7), or fertilizer all can
weaken the root system of trees and shrubs. An excess or deficiency
of water, in particular, can lead to permanent root damage. Ash,
birch, honeylocust, maple, oak, and sweetgum trees are particularly
sensitive to an excess or deficiency of water.
Trees and shrubs planted im-properly or in unfavorable locations
will also be stressed by poor root growth and development. Planting
trees and shrubs too deeply or incorrectly (Figure 6) or in sites
with poor drainage, mineral deficiencies or imbalances, a soil reaction
(pH) that is too alkaline, poor soil type, or soil compaction should
be avoided. Paved sidewalks, driveways, streets, building foundations,
patios, septic tanks, and other obstructions can greatly restrict
the growing space for proper root development. If a balance between
the crown and root system cannot be maintained, the tree or shrub
will be weakened, and decline and dieback may develop a few years
Because so many factors can cause decline and dieback, the primary
causes are listed below in the approximate order of general frequency:
1. Poor soil structure and drainage (important when the soil is
2. Herbicide injury to foliage, roots, or other parts (Figures 3
3. Poor transplanting procedure and lack of proper maintenance
after transplanting (Figure 6).
4. Construction damagecutting and removal of roots (Figure
5. Significant damage to trunk or major limbs (mechanical injury
from lawn mowers, vandalism, vehicles, squirrels and other rodents,
livestock, etc.) (Figure 2).
6. Repeated defoliation by insects or diseases, especially such
leaf disorders as scorch, anthracnose , rust, and leaf spot or needle
blight (Figure 3).
7. An extended drought in combination with high temperatures and
strong southerly winds
8. Vascular diseasessuch as Verticillium wilt, oak wilt,
or Dutch elm disease (Figure 3).
9. Soil nutrient deficiencies
10 Insect borer injury to the trunk or branches.
11. Canker disease(Figure 3).
12. Excessive soil moisture
13. Extremely low winter temperatures or a rapid change in temperatures
14. Poorly formed or girdling roots (Figures 2 and 6).
15. Soil compaction from vehicles or heavy construction equipment
16. Fungal root and trunk decays such as Armillaria root rot (Figure
17. Lightning injury
18. Soil fill or removal (Figures 1 and 5).
19. Bacterial wetwood and slime flux
3. Red maple killed by rapid drop in temp after mild weather
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4. Many diseases on this "sick" tree could result
in decline and dieback. All diseases would not occur on the same
tree. Diseases are: 1. Root-lesion nematode; 2. root-knot nematode;
3. root pruning by nematodes; 4. stubby-root nematode injury;
5. root rot; 6. crown gall; 7. fruiting bodies of Armillaria root
rot fungus; 8. fruiting body of Ganoderma wood and root rot fungus;
9. fruiting bodies of Fomes wood rot fungi; 10. trunk canker;
11. cedar-quince rust on hawthorn; 12. cedar-hawthorn rust; 13.
cedar-apple rust; 14. mosaic; 15. downy mildew; 16. apple scab;
17. leaf spot; 18. powdery mildew; 19. black knot of plum and
cherry; 20. wetwood (slime flux); 21. fire blight; 22. American
mistletoe; 23. 2, 4-D injury; 24. witches' broom; 25. fruit rot
(apple); 26. overwintering canker of fire blight; 27. wilt; 28.
leaf curl or blister of peach, cherry, or plum; 29. leaf blister
(oak); 30. sooty blotch and flyspeck of apple; 31. leaf blotch;
32. shothole; 33. anthracnose; 34. ringspot; 35. sooty mold; 36.
tar spot; 37. leaf scorch; 38. apple scab on fruit; 39. twig and
branch canker (drawing by Lenore Gray).
The exact cause or causes of decline and dieback needs to be identified
so that corrective steps may be taken. Accurate diagnosis is often
difficult however, especially on older trees. Usually an on-site
examination of the diseased tree is required to assess the influence
of the environment and to inspect for foliage, branch, trunk, and
root problems. Laboratory examination of diseased leaf, twig, or
branch specimens may confirm that an infectious disease problem
exists (Figure 3). A careful examination of the roots, trunk, and
soil conditions can reveal some basic causes for decline. In some
cases, a precise diagnosis can be made only by a combination of
field and laboratory examinations. It is very important to consider
both the site and the past care given the plant. The following
steps, as well as the answers to the questions posed, may help to
determine the underlying cause or causes of the decline and dieback.
1. Determine the case history of the plant and general area: Has
severe and repeated defoliation by insects, disease, or another
cause occurred in recent years? Has severe drought or other adverse
weather factors affected the plant in recent years? Has the soil
been saturated or flooded for extended periods? Has there been construction
work near the tree in recent years causing trunk or root damage,
soil compaction, or soil deterioration? Has there been soil or root
removal? Has there been soil fill? (If unknown, observe whether
the normal trunk flare is visible at the soil line. If not, determine
the depth to the buttress roots.) Has the water table in the area
changed? The use of a soil profile tube is essential in making many
of the observations concerning soil problems.
2. Examine nearby vegetation: Is there evidence of injury to surrounding
trees, flowers, shrubs, vegetables, fruits, turfgrass, or weeds
that would suggest general environmental (Figure 2) or toxic symptoms?
Is the tree or shrub's root system subject to salt accumulation
from winter ice control along nearby sidewalks or streets? Is there
a toxic sewage disposal field or gas line near the root system that
may be leaking?
3. Consider chemical treatments to or near the tree or shrub: What
is the history of pesticide use, particularly herbicides or "weed
and feed" combinations? Was a soil sterilant or biocide used
in a nearby gravel driveway or sidewalk?
4. Examine leaves for foliar diseases and insects.
5. Eliminate the possibility of a vascular disease, that is, oak
wilt, Dutch elm disease, Verticillium wilt, or mimosa wilt, by considering
the pattern of symptom development and by examining for internal
6. Have a professional arborist determine the year(s) or period(s)
of tree stress by examining the amount of twig growth and the width
of growth rings in the wood. Also have the arborist check the pattern
of annual stem elongation to determine if and when growth has slowed
or stopped. (The arborist will examine the growth of annual rings
over the last several years with an increment hammer or borer.)
7. Examine branches and trunk for extensive cankers that may be
the cause of damage or that may be associated with an environmental
or other stress.
8. Examine trunks and buttress roots for evidence of injury, for
example, a sunscald, fire, mower, frost crack, or lightning injury.
Look for loose bark (tap the bark and exposed roots and listen for
a telltale hollow sound). Check for mushrooms or conks of wood and
root decay fungi. Fungal fruiting structures are most common in
spring and fall following periods of wet weather.
9. Carefully excavate the buttress roots for evidence of fungal
decay, poorly formed roots, girdling roots or twine, and similar
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