Some copper fungicide couldn't hurt, hey?
actually it could, if it did not kill bacteria and went into the soil it could kill beneficials.
By Guy Meilleur
“Roll out those lazy, hazy, crazy
days of summer; those days of
soda, and pretzels and beer!” as
Nat King Cole sang way back when.
Summer is also the time for other foamy
stuff, the kind that has certain insects
singing songs of cheer. However, this is not
good news for unfortunate older trees that
serve as taverns for moths and hornets and
other imbibing creatures.
Finding these frenzied congregations on
oozing, stinking, discolored areas on the
lower trunks of older trees often incites tree
owners to call arborists this time of year.
But insecticide is not the answer, because
the insects are only a sign of trouble underneath
the bark. Oozing slime is a symptom
of bacterial infection, and “… warm temperatures
are favorable for the
development of some bacterial diseases
…” as John Lloyd notes in Plant Health
Care for Woody Ornamentals.
A coating of polysaccharide, which is
called a “slime layer” for obvious reasons,
surrounds bacterial cells. When the bacteria
multiply, they are forced out of the host
plant and ooze down the bark. Dividing as
fast as once every 20 minutes, they quickly
build up their numbers to as high as a
billion per milliliter. A cocktail of bacteria
– Pseudomonas, Enterobacter, yeasts and
other organisms – causes slime flux disease.
Whether any of these organisms is
particularly pathogenic (or it is simply the
physical pressure caused by all of them
multiplying) that kills the bark is not clearly
understood. Fermentation produces
gases, such as methane and carbon dioxide,
that increases the pressure that ruptures the
bark. Many different microorganisms grow
in the flux, producing an indescribably foul
or alcoholic odor that is hard to miss.
Different species of trees have different
types of slime flux disease. The types
found higher up in wounds and crotches of
elms and poplars are considered relatively
benign. They seldom seem to damage the
Bacteria and gas bubble through the bark between the buttresses. Finding frenzied congregations of insects on oozing, stinking, discolored areas on the lower trunks of older trees often
incites tree owners to call arborists. Insecticide is not the answer, because the insects are only a sign of trouble underneath the bark. Photos courtesy of Guy Meilleur.
TREE CARE INDUSTRY – SEPTEMBER 2004 33
bark aggressively. What damage occurs is
well above ground level and considered
correctable. They are located in Zones 2
and 4 as defined in Dr. Kim Coder’s
“Hazard Tree Evaluation” form, published
in 1990. On older oaks the disease is quite
different; it is typically found between buttress
roots. This is Zone 1, where damage
and disease are considered critical.
Previous physical damage or previous
insect injury is seldom noted at infection
sites on the trees studied. Similar to
included bark in a crotch, the bark between
buttresses seems to be squeezed. One theory
is that the tree opens itself up to
infection by wounding itself when bark is
included, and the bacteria enter from the
soil. This is addressed by Dr. Alex Shigo
in Modern Arboriculture, in which he
states that, “Included bark between roots
and root stubs are common underground
infection courts.”
To act or not to act
The old practice of drilling into the
infection and installing a drain pipe to
direct the slime flux away from the bark
can expand the infection court and worsen
the disease. The wet, alkaline conditions
at these sites is inhospitable to most
decay-causing fungi, so one thought is to
leave well enough alone. When armillaria
fungus is found along with slime flux,
more rhizomorphs are found outside the
oozing areas. Only a few stunted “shoestrings”
are found in the slime. Many
insects that are harmless to the living tree
– ants, termites, centipedes and sowbugs,
for instance – can be found under the dead
bark, but there is no reason to go after
them. However, carpenterworms,
Prionoxystus sp., are also active in these
infection sites. As Warren Johnson and
Howard H. Lyon report in Insects that
Feed on Trees and Shrubs, “Over a period
of time, the activities of the carpenterworm
larvae may prove disastrous to the
host tree …” The need to expose and treat
this pest calls for the removal of dead
bark. Bacterial activity and slime flux on
older oaks can and does kill cambium,
expanding the diseased area every year.
So there is also a clear need for noninvasive
methods to preserve the tree.
The first job is to find out which portions
of the bark are dead. The initial cues are
visual – lesions bleeding with blackened
sap at the margins of the diseased area.
These lesions appear very similar to those
caused by infections of fungi, such as
Phytophthora sp. Auditory cues are gained
by tapping with a rubber or plastic mallet
outside these lesions. A solid sound indicates
living bark over solid wood. Tapping
inside the lesions will produce a hollow
sound, indicating dead bark. A stethoscope
can be used to hear the sound better, but is
often not necessary to detect dead bark.
The next step is probing these areas with a
blunt instrument, such as a trowel or
screwdriver. Remove all discolored bark
down to the wood. In some cases this
means removing a lot of bark. If the infection
encompasses more than half of the
trunk and decay is advancing inward, it is
doubtful the tree will remain safe for very
long. It is probably best to treat these
unfortunate trees with a chain saw at
ground level.
Slime was seen fluxing here in 1998, but it was untreated. Removal is now required.
Bacterial activity and
slime flux on older
oaks can and does kill
cambium, expanding
the diseased area
every year. So there is
also a clear need for
noninvasive methods
to preserve the tree.
Cut around the infected trunk or branch
until you come close to healthy cambium.
Take care not to cut into healthy bark or
wood. Excavation of wounds is still
viewed with skepticism in some circles
precisely because of the fear that careless
digging will result in more damage. When
most of the dead bark has been removed, a
sharper tool will trim the edges of infected
material. In “Helping Plants Survive
Armillaria Root Rot” (November 2003
issue of Tree Care Industry), author J.
Harold Mitchell describes the excavation
of tissue infected with the fungus
Armillaria. Because bacterial infections
seem less virulent and do not cause wood
decay like Armillaria does, a more cautious
approach to tissue removal seems to be
warranted. The goal is to come as close as
possible to healthy tissue without cutting
into it. A blunt-tipped knife, such as a
linoleum knife, can trim the last scraps of
diseased bark without scratching the wood.
There is no need to trace the wound into an
oval, because sap can flow laterally within
the cambium. Careful removal of dead
bark may reveal the cambial layer, still
light in color and adhered to the wood. The
more living cambium that is left, the sooner
the tree can close its wounds. Rinsing off
the last of the debris with a sharp stream of
water from the garden hose or better yet a
jet of air from a pneumatic tool will finish
the excavation work.