Dieback & Decline

DIEBACK AND DECLINE

Bruce R. Fraedrich, Ph. D., Plant Pathologist

The term “dieback” technically refers to the
progressive dying-back of shoots and
branches from the tip downward, while the
term decline refers to the progressive
deterioration of an entire tree. These terms,
however, are often used interchangeably to
denote the general deterioration of an
individual tree, or entire species of trees.
Tree showing early stages of decline that
typically starts in the upper canopy
Dieback/decline of individual trees is fairly
common in a shade-tree environment where
a particular tree has received little or no
care. Under certain conditions, however,
large-scale decline or dieback may affect a
particular tree species in a given geographic
area. Maple, oak, ash, birch and boxwood
are currently experiencing this phenomenon
in various sections of the Eastern United
States.

SYMPTOMS
Initial symptoms of dieback/decline are
often very difficult to detect to the casual
observer. General reduction in growth,
chlorotic foliage, slight twig mortality,
premature fall coloration and defoliation,
and abundant fruit and flower production,
often characterize the initial stages. As the
disease progresses, the foliage becomes
dwarfed and tufted at the ends of the twigs.
Twig and branch mortality becomes more
severe, and an overall thinning of the crown
is evident.
Advanced stages are characterized by
extensive branch mortality. Cankers are
commonly evident on the branches as well
as the main stem, and root and butt decay
often occurs. Attack by insect borers may
occur as well. Declining trees may linger for
a seemingly indefinite period, or death may
occur within just two or three years following
the onset of symptoms.
CAUSE
Dieback/decline is a complex disease,
which cannot be attributed to any single
factor. This disease most often results
when trees are weakened by an initial
stress factor. Although there are many
factors, which can cause this initial stress,
root or soil disorders are the most common
causes. Some causative disorders include
girdling roots, soil compaction, changes in
the depth of the water table, deicing salts
leached into the root system, low soil
nutrients and low or excessive soil moisture.

Other stress factors include repeated
defoliation due to leaf-feeding insects or
foliar pathogens, air pollution damage,
misapplied pesticides and fertilizers,
mechanical wounding from automobiles,
lawn mowers, etc., and lightning strikes.
Where the initial stress factor occurs over a
large geographic area, an entire species
may die back or decline.
Once the tree is sufficiently weakened,
secondary fungal invaders or boring insects
commonly attack the tree, which results in
its death.
CONTROL
Dieback/decline can best be controlled
through preventing the occurrence of the
initial stress. Cultural practices including
periodic fertilization, pruning, watering
during dry periods, and control of leaffeeding
insects and foliar pathogens are
essential in preventing the onset of the
dieback/decline complex. Proper initial
selection of plant species and planting sites,
as well as strict adherence to correct
planting techniques, are also primary
considerations in preventing this disease
condition.
Proper mulching to the dripline is one
cultural practice that both avoids and helps
correct decline symptoms
Control of dieback/decline is much more
difficult once a tree is affected. The primary
stress factors must first be determined and
corrected. This is often complicated by the
presence of secondary insects or fungal
invaders, which are often mistakenly
implicated as the primary cause of the
problem.
Knowing such factors as past weather
conditions, activities in the area and cultural
practices performed on the tree are usually
necessary in determining the initial stress
factor. Once these factors have been
determined, the cultural practices as
outlined above should be carried out
regularly.
Fertilizer application should be based on
results of laboratory soil tests.

If you have questions on the condition of your tree or suspect that it could be declining, call Hansen’s and ask for a certified arborist to evaluate your trees.