This item is only available as the following downloads:
Combined Forest Pest
Home and Garden Bulletin
JNI'v .. L Li
DOCUMEN DE .
How it Hurts
S- o .. .\
I ,I .r r- ,
4 JAN .d
e .&. '
Defoliation by the Gypsy
How it Hurts Your Tree
Philip M. Wargo1
In 1974 the U.S. Department of
Agriculture initiated the
Combined Forest Pest Research
and Development Program, an
interagency effort that
concentrated on the Douglas-fir
tussock moth in the West. on the
southern pine beetle in the South,
and on the gypsy moth in the
Northeast. The work reported in
this publication was funded in
whole or in part by the program.
This manual is one in a series on
the gypsy moth.
Leaves are a pleasant background
for our houses and provide relief
from a hot sun. They also act as air
filters by removing dust and
pollutants from the atmosphere,
and buffer our ears from the noises
generated by our daily activities.
Leaves also provide beauty and
color throughout the year. The
main purpose of leaves, however,
is to produce food for the tree so it
can produce wood and more leaves
for the next year.
Defoliation caused by hungry gypsy
moth caterpillars (larvae) eating the
leaves may deprive us of a tree's
beauty and benefits temporarily for
1 or several years (figs. 1 and 2).
But we might be left permanently
without these benefits, because
defoliation can result in dead,
leafless trees (fig. 3).
Figure 1.-Ragged foliage that
has been chewed by the g. p,-
' Research plant p.ithologit. Forest Insect
& Disease Research laboratory, Hamden.
When an oak tree (the primary food
source of the gypsy moth) loses its
leaves for any reason other than
the onset of winter, its natural
growth and food-making cycles are
interrupted. The tree may not
produce enough food and may have
to use its food reserves. This can
weaken the tree, leaving it
vulnerable to attack by insects and
Figure 2.-Closeup of the g. ps,.
moth caterpillar in its later
growth stages when it is fairly
Whether a tree ends up as a cutoff
stump or a functional living tree
after defoliation depends on how
badly the tree was affected by
defoliation, and this depends on:
* How much foliage was eaten
* If the tree refoliated
* How many years in succession
the tree was defoliated
* When during the year defoliation
* What the weather conditions
were after defoliation
* If disease organisms and other
insects attacked the tree
* How healthy or vigorous the tree
\,., before defoliation.
These criteria are discussed in this
booklet. When you finish reading,
you should understand why
defoliation hurts your tree and have
some idea about your tree's
chances for survival if it has been
defoliated by the gypsy moth.
While this booklet does emphasize
defoliation of oak trees by the
gypsy moth, the information applies
to defoliation of other deciduous
trees (a tree that sheds its leaves
each autumn) and to other insects.
Figure 3.-Oak trees that have
died after heavy gypsy moth
defoliation. Oaks in foreground
have been cut down for firewood.
1. How much foliage was eaten?
One of the most important factors
is how much foliage was eaten by
the gypsy moth caterpillar. The
more foliage the insect eats, the
less food is produced for the tree
The worst situation for the tree is
when all the foliage has been eaten.
With all the leaves gone, the tree
has no food-producing system, and
it must live off its reserve foods
until the new leaves appear. These
reserve foods are used normally to
feed the tree during the winter
resting period. If the tree enters
winter with low food reserves,
some parts of the tree may die.
Apparently a tree can lose up to
half its foliage before it begins to
suffer. When more than half the
foliage is eaten, the tree begins to
change because not enough food
and other growth substances are
Figure 4.-Oak trees in various
stages of defoliation: A, No
defoliation: B, light defoliation:
C. moderate defoliation: D,
2. Did the tree refoliate?
At some point, enough tree leaves
are eaten to cause the tree to
produce new leaves-refoli ation-
and this is bad for the tree. The
tree then behaves as if autumn and
spring have arrived together. The
remaining pieces of leaf and leaf
stems are shed just like they are in
autumn, but without a color
change. Then, the changes that
bring a tree from the resting state
to full leaf in the spring occur
again. In 2 to 3 weeks, new leaves
begin growing. This "spring again"
condition may be necessary for the
tree to survive, but because reserve
foods are used, it puts a
tremendous strain on the tree.
Even with the new leaves, the tree
is still at a disadvantage. The new
leaves are only half the original size
and are fewer in number than
before defoliation (fig. 5). The new
leaves are usually a lighter green,
which indicates that there is less
chlorophyll in them (chlorophyll is
the substance that converts light
energy from the sun to sugar
energy for the tree). The new
leaves are probably producing less
energy for the tree and have a
shorter growing season, too. These
problems may still be present the
The shortage of energy causes the
tree to respond in several ways.
The most obvious is the dieback of
twigs and branches that occurs
especially during the winter months
and that becomes evident in the
spring. Usually the top twigs and
Figure 5.-(omparison of an
undefoliated tree (A) with a
defoliated/refoliated tree (B).
Notice that the leaves are a
lighter green, smaller, and fewer
in number on the refoliated tree.
branches die first. When tip
branches die, old buds on the older
branches sprout; in severe cases
this sprouting occurs on the larger
branches and trunk and makes the
tree unattractive (fig. 6).
On living branches, the amount of
new twig growth is less than
normal-sometimes only one-tenth
as much as on undefoliated trees.
Internal growth is also affected: less
wood is produced in the annual
ring. This is not so important to
people who own trees mainly for
shade or beauty, but to foresters
who grow trees for wood products
it can mean considerable economic
Roots depend on the leaves for
food, too. When defoliation reduces
food production, many small feeder
roots can die. These roots absorb
minerals and most of the water
needed for tree growth. With fewer
feeder roots, fewer minerals and
less water are absorbed and sent to
the leaves, and food production by
the leaves is lowered even more.
Figure 6.-An oak tree showing
the effects of defoliation and
sprouling of the tree in response
to branch death in the top of the
3. How many years in succession
has defoliation occurred?
One year of defoliation is bad, but
2 or 3 years of defoliation is worse.
Even defoliation that does not
cause the tree to refoliate is
harmful if it is repeated for several
years. A weak tree often suffers
after only one season of defoliation.
But even a healthy tree can die if
defoliated 2 or 3 years in a row,
especially if the tree refoliates each
time it is defoliated. A defoliated
tree begins the new season with a
considerable handicap, and a repeat
performance weakens the tree
further and lessens its chances for
4. When during the year was the
No time is right for defoliation, but
the best time would be either very
early or very late in the growing
season. Early defoliation gives the
tree a longer time to recover before
natural autumn defoliation occurs.
Defoliation late in the season is less
harmful because the tree has
completed most of its growth, has
stored most of its food, and is
getting ready to do its normal
autumn shedding. Also, the tree
usually won't refoliate this late in
the season even if all the foliage is
eaten. However, several years of
defoliation even at these less
critical times can still be bad for the
The worst time for defoliation is 4
to 6 weeks after buds open in the
spring, when the tree is growing
rapidly and food reserves in the
shoots and roots are lowest.
Unfortunately, this is exactly when
the gypsy moth is doing most of its
feeding. With such low food
supplies, the tree cannot feed all its
branches and roots until new leaves
are formed; some die, and the tree
5. What were the weather
conditions after defoliation?
How badly a tree is weakened
depends on how quickly new leaves
are formed and how much food
they produce. Both are influenced
by the growing conditions or
weather. Too much rain during
refoliation may set the stage for leaf
diseases caused by fungi (fig. 7),
and the tree may be defoliated
again in the same season.
Dry weather is just as bad. If a tree
lacks moisture during refoliation,
leaf growth is poor. and these small
leaves produce less food. If dry
weather continues, food production
is lowered because leaves need lots
of water to manufacture food. If
dryness occurs with high
temperatures, leaves may also be
Figure 7.-Leaves of white oak
hsho% ing symptoms of a fungus
6. Did disease organisms and other
insects attack the tree?
The death blow to many trees after
defoliation comes from organisms
we call "opportunists." They take
advantage of the weakening effect
that defoliation has on a tree. If the
tree had not been defoliated, these
organisms would not succeed in
attacking the tree. One such
organism is a root-attacking fungus
called shoestring root rot, which
forms black shoelacelike structures
on the surface of the roots and in
the soil (fig. 8). Weak, dead, or
dying roots may provide entrance
places for this fungus, which can
then kill other roots. The fungus,
which grows in the food-and-water-
carrying tissues of the roots,
restricts the amount of water and
minerals that is carried to the
leaves and prevents food from
going to other roots (fig. 9). The
results are more dead roots and
greater water and nutrient
Figure 8.-Section of root
'ho% ing the black shoelringlike
structures of the shoestring root
rot fungus growing on the bark
Figure 9.-Dead oak tree with
white fans of the shoestring root
rot fungus growing on the wood.
Fans were exposed by peeling off
the bark (right foreground).
An insect that takes advantage of
primarily oak trees weakened by
defoliation is the twolined chestnut
borer (fig. 10). This insect attacks
the branches and trunk of the tree
and chews feeding tunnels in the
tissues that move food, water, and
minerals to the shoots and roots
(fig. 11). These tunnels prevent
water, food, and minerals from
moving to w here they are needed,
which causes more leaves,
branches. and roots to die.
Figure 10.-Four growth stages
the twolined chestnut borer larva.
which tunnels in the bark and
wood of defoliated oak trees.
The combination of the fungus in
the roots and borers in the shoots
will obviously result in a dead tree.
In many instances a tree will die
rapidly, especially late in the
summer during hot, dry weather.
The leaves suddenly turn brown
and the tree dies (fig. 12).
Unfortunately both of these
organisms operate hidden beneath
the bark (figs. 9 and 11), and by the
time they are visible, the damage
has been done. Currently there is
no effective way to keep the fungus
from attacking the roots or to kill
the fungus once it enters the roots,
but the borer can be controlled
Figure 11.-Dead oak tree
showing the feeding tunnels
created by larvae of the twolined
chestnut borer. Tunnels were
exposed by removing the bark.
Figure 12.-Tree showing
symptoms of twolined borer and
shoestring fungus attack. Leaves
brown suddenly during hot. dry
weather, usually in August, and
the tree then dies.
7. How healthy or vigorous was the
tree before defoliation?
But even in the presence of
"opportunistic" organisms and
after several successive years of
severe defoliation, a tree can
survive if it was in good health
when defoliated. Stresses such as
drought, soil compaction, or
disturbance during construction can
weaken a tree. These stresses
interfere indirectly with food
production and may reduce the
amount of stored food reserves or
even cause some twig and root
death. A tree weakened by stress
will be more vulnerable than a
healthy tree to the effects of gypsy
How can you help your tree
tolerate defoliation? First and
foremost, keep your tree healthy.
Water and fertilize it properly.
especially during stress conditions
such as drought. Try to avoid other
stress inducers such as soil
competition from turf grasses. or
intrusions from driveways and
sidewalks. When you plant a new
tree, avoid these situations and
conditions that cause stress to the
tree. Give the root system adequate
growing room and mulch it for
proper aeration of the roots. If
possible. keep a mulched area
around the tree. Plant the proper
tree in the proper place, and
consult professionals if you aren't
sure. Cared-for trees are healthier
and will tolerate defoliation better.
Protect your tree from being
defoliated with carefully applied,
commrcicilly safe insecticides. If
the tree is small, the caterpillars
can be picked off. If your tree gets
defoliated in spite of your efforts
and it refoliates. care for it during
refoliation. If moist conditions
prevail, be prepared to spray the
leaves with fungicide at the first
sign of leaf disease. In very dry
weather, water your tree Nwhile it is
refoliating to help early leaf growth
and encourage healthy leaves.
Fertilize your tree in the fall or
early spring before leaves appear to
help replace minerals lost during
Figure 13.-Adult beetle of the
twolined chestnut borer. which
lays eggs on the bark of oak trees
in late spring and early summer.
Note the two red-brown lines on
the wing covers,. from which the
borer gel- its name.
Borer attack can be reduced by
spraying the branches and trunk of
the tree with an insecticide
registered for use against borers.
Spraying should be done during the
month of June, when the beetle
stage of the borer is laying eggs on
the bark surface (fig. 13).
By applying these measures, your
tree should survive a defoliation
even if it loses all its leaves and
refoliates. But once your tree has
been defoliated, take extra
precautions not to let it happen
again next year.
The author thanks Dr. Robert
Talerico, Roger Zerillo. and
Richard Rollinson. Gypsy Moth
Program. Hamden, Conn., for
photographs of larvae and
defoliation, and Dr. Wilfred Cote.
International Paper Co., Tuxedo
Park, N.Y., for photographs of the
twolined chestnut borer.
Issued January 1978
For Sale by the Superintendent of
U.S. Government Printing Office
Washington, D.C. 20402
Stock No. 001-000-3747-1
UNIVERSITY OF FLORIDA
II ll 111126 II 08584 2937
3 1262 08584 2937
xml version 1.0 encoding UTF-8
REPORT xmlns http:www.fcla.edudlsmddaitss xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.fcla.edudlsmddaitssdaitssReport.xsd
INGEST IEID E14837Q1C_X99PX0 INGEST_TIME 2012-02-29T18:13:21Z PACKAGE AA00009163_00001
AGREEMENT_INFO ACCOUNT UF PROJECT UFDC