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SUDDEN
OAK DEATH IN TEXAS Texas is currently considered
a low-risk area for SOD because it is believed the pathogen prefers cool moist
environments like that of coastal California.
Confirmed in Texas: In 5 nurseries that
have received nursery stock from Monrovia
INTRODUCTION
Oak mortality is caused by a new
pathogen, Phytophthora ramorum
Sudden Oak Death (SOD) is a newly discovered, highly infectious disease
caused by a fungus-like organism
 within the genus
Phytophthora. The disease was first discovered in Northern California in 1995
where it has since been implicated in large-scale oak mortality. It is estimated
that tens of thousands of tan oaks, coast live oaks and black oaks have been
killed on the west coast so far.
The pathogen was isolated and identified in 2000 by researchers from the
University of California as
Phytophthora ramorum. This is
an organism that has previously only been known to exist in Germany and the
Netherlands, where it was found infecting Rhododendrons and Viburnums.
THE DISEASE
What is Sudden Oak Death?
Sudden Oak Death has been classified as an invasive species. These organisms
are of great concern because history (by the U.S. Department of Agriculture
Animal and Plant Health Inspection Survey - APHIS) has shown that an introduced
species has the potential to spread easily with devastating effects. Introduced
species often have no natural enemies and have potential hosts with no
ecologically adapted defenses.
There are numerous examples of introduced tree pathogens and insects that
cause devastating problems including chestnut blight, dutch elm disease, gypsy
moth caterpillars, white pine blister rust, hemlock woolly adelgid, and fusiform
rust.
Given the severity of the effects that invasive species can cause it is
justified to give the Sudden Oak Death situation very serious attention.
The common name "Sudden
Oak Death" may be misleading due to both the words "sudden" and "oak". The
common name was given because of the apparent rapid decline in crowns of
infected oak trees, changing from green to brown in sometimes a matter of just a
few weeks. But researchers do not yet know how long the disease actually
progresses before death. Also, many infected hosts do not decline "suddenly", or
even die at all. The disease seems to manifest itself and progress differently
depending on many factors including individual tree characteristics, site
factors and the species.
The term "oak" in Sudden Oak Death may be misleading because it does
not reflect the potential that this disease has for causing serious problems in
a wide variety of potential non-oak hosts.
SOD not only causes severe cankering and rapid death of oaks, but has
been found causing foliar and twig blights on numerous other trees and shrubs.
There are at least 14 different species of ligneous hosts known to be affected
by P. ramorum (for current list, see hosts). Many of these hosts, such as those
in the genera Quercus, Arbutus, Acer, and Rhododendron have valuable
counterparts in native and planted Texas landscapes.
There are many aspects of SOD that are poorly understood For example,
the origin of the California outbreak disease is still unknown. There is no
information on how long the disease has been on the West Coast, but there is
some speculation that it may have been there for quite awhile and the damage is
just now escalating due to the accordance of predisposing stress. Changes in
environmental conditions such as climatic change, fire suppression, and
alterations in land use patterns have all been implicated in the epidemic.
The array of symptoms observed on different hosts currently cannot be
explained and there is an unaccountable variable mortality rate among infected
plants.There is also some speculation that it originated in Europe and perhaps
transported on infected rhododendrons, but there is no direct evidence yet to
support this claim. So far, there is no 'cure' yet for SOD, although research is
being conducted in this area.
Although SOD has not yet been identified in the United States outside
of California and Oregon, laboratory studies have shown that many species
outside the current distribution are potential hosts, including eastern and
northern red oak, and pin oaks. The spread of Sudden Oak Death to other parts of
the country must be considered, given that the pathogen can be moved great
distances by transport in nursery stock such as SOD infected rhododendrons, or
in soil and bark products.
For more information about
"Sudden Oak Death" at Texas A & M University, contact Dr.
David Appel at 979-845-8273 or by e-mail at
appel@ag.tamu.edu
or Sara Service at 979-587-2701 or by e-mail
s-service@neo.tamu.edu
Key
Points
· Phytophthora ramorum is a newly discovered pathogen, and very
little is known about it. There is a great deal of research currently being
conducted on the disease and there are national monitoring plans being
initiated.
· It is believed that the pathogen can be transported from
location to location easily by way of infected nursery stock, soil, and bark
from SOD infected areas.
· Phytophthora ramorum has not been detected outside of coastal
California and Oregon.
· SOD affects a wide variety of hosts, not only oaks but several
other species of trees and shrubs as well.
· There are a wide variety of symptoms associated with SOD
including bleeding cankers, twig blights and foliar leaf spots.
· Texas is currently considered a low-risk area for SOD because
it is believed the pathogen prefers cool moist environments like that of
coastal California.
· Not all infected hosts die from SOD. Mortality is most likely
among the oaks.
HOSTS
It is important to note that none of the following known hosts are
common to Texas. These plants are all indigenous or adapted to the ecology of
central California and Oregon. However, the list of susceptible hosts is
expanding, and many of these known susceptible host species have relatives in
native and planted Texas landscapes.
Known Phytophthera ramorum Hosts
In Texas there are ten plant genera that this pathogen are known to
infect. They are Acer, Aesculus, Arbutus, Pseudotsuga, Quercus, Rhamnus,
Vaccinium, Vibunum, Castanea and Fagus. These are the suspect hosts in Texas
that are being looked at for those nurseries that have received stock from
Monrovia.
SYMPTOMS on Trees
  
 
· Brown
to Black Cankers on lower trunk
·
Occasional cankers on higher
branches
·
Oozing dark red to black sap
· Cankers on some
species may not bleed
·
Healthy appearing crown in the
early stages
·
Later stages: thinning or
complete browning of crown
·
Browning of leaves may occur
over a period of weeks
·
Beetles and Hypoxylon fungus
often move opportunistically into SOD weakened trees
·
Twig dieback on some species
·
Spontaneous drooping of new
growth on some species (tanoak)
·
When the outer bark is removed,
a dark zone line is evident delimiting healthy tissue from necrotic tissue
Symptoms
on Foliar (non-oak) Hosts
  
·
Leaf spots
·
Twig dieback
SOD on
foliar hosts can only be identified by laboratory analysis
Prepared by:
Joseph G. O’Brien, USDA Forest Service, Northeastern Area
Manfred E. Mielke, USDA Forest Service, Northeastern Area
Steve Oak, USDA Forest Service, Southern Region
Bruce Moltzan, Missouri Dept. of Conservation
Oak Disorders That Resemble
Sudden Oak Death
In eastern hardwood forests, sudden
oak death can be confused, in particular, with oak wilt, oak decline, and
red oak borer damage. Descriptions of these disorders and comparisons with
sudden oak death follow.
Oak Wilt |
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 Oak
wilt is an aggressive fungus disease caused by Ceratocystis fagacearum.
It is one of the most serious diseases in the Eastern United States,
killing thousands of oak trees in forests, woodlots, and home landscapes.
Susceptible hosts include most oaks in the red oak group and Texas live
oak. Symptoms include wilting and discoloration of the foliage, premature
leaf drop, and rapid death of the tree within days or weeks of the first
symptoms. Trees become infected with oak wilt in two ways: through
connections between root systems of adjacent trees, and through insects
that carry the fungus to other trees that have been wounded.
Similarities: Oak wilt can also kill trees
very quickly, especially if infection begins through root grafts.
Differences: The oak wilt pathogen does not cause cankers on the stems,
and no bleeding is associated with this disease. Dark staining may be
evident under the bark of trees with oak wilt, but there are no
conspicuous zone lines. Oak wilt typically causes red oak leaves to turn
brown around the edges while the veins remain green. Leaves are rapidly
shed as the tree dies. Conversely, in live oak with the sudden oak death
pathogen, the veins first turn yellow and eventually turn brown. Leaves
are often retained on the tree after it dies.
| Oak Decline |
|
 Oak
decline is a slow-acting disease complex that can kill
physiologically mature trees in the upper canopy. Decline results
from interactions of multiple stresses, such as prolonged drought
and spring defoliation by late frost or insects, opportunistic root
disease fungi such as Armillaria mellea, and
inner-bark-boring insects such as the twolined chestnut borer and
red oak borer. Progressive dieback of the crown is the main symptom
of oak decline and is an expression of an impaired root system. This
disease can kill susceptible oaks within 3-5 years of the onset of
crown symptoms. Oak decline occurs throughout the range of eastern
hardwood forests, but is particularly common in the Southern
Appalachian Mountains in North Carolina, Tennessee, and Virginia, as
well as the Ozark Mountains in Arkansas and Missouri.
Similarities: Oak decline can cause death of many oaks on a
landscape scale. Moist, dark stains may be present on the trunk of
trees affected by oak decline. Differences: Oak decline shows
evidence that dieback has occurred over several years from the top
down and outside inward. Newly killed branches with twigs attached
are usually found in the same crown as those in a more advanced
state of deterioration killed years before. Dieback associated with
sudden oak death occurs over a growing season or two. The inner bark
beneath the dark stain associated with stem-boring-insect attacks
has a discrete margin with no zone lines or evidence of canker
development beyond the attack site.
| Red Oak Borer |
|
 Red
oak borer (Enaphalodes rufulus (Haldeman)) attacks oaks
of both red and white groups throughout the eastern United
States, but prefers members of the red oak group; however, it
does not kill trees. Outbreaks are associated with stressed
trees that eventually die from oak decline. The complete life
cycle takes 2 years. Adults are 1-1.5 inches long with
antennae one to two times as long as the body. Larvae are the
damaging life stage. Adult females lay eggs in mid-summer in
refuges in the crevices of the bark. Newly hatched larvae bore
into the phloem, where they mine an irregular burrow 0.5-1
inch in diameter before fall. In spring and summer of the
second year, dark, moist stains and fine, granular frass may
be seen on the trunk. Exposure of the inner bark reveals the
frass-packed burrow and the larva, if it has not bored more
deeply into the wood to complete development. Mature larvae
are stout, round-headed grubs about 2 inches long before they
pupate deep in the wood.
Similarities: Moist, dark stains and fi ne frass may be
present at sites of red oak borer attack. Differences: With
red oak borer the inner bark beneath the dark stain contains a
frass-packed burrow and has a discrete margin with no zone
lines or evidence of canker development beyond it.
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(Slime
Flux) in Trees
Dark amber liquid Ooze
bleeds out of canker wound
Description and Diagnosis
Bacterial wetwood involves a liquid that oozes and bubbles
through the bark cracks and wounds, also known as slime flux,
inspired by the slimy, foul smelling, brown appearance of the
liquid. The prime wounding agents are insect borers,
mechanical injury, and natural cracks and splits which are
rarely observed. This condition is common in oaks, mulberry,
sycamore, elm, ash and redbud. There are several common types
of anaerobic soil bacteria
(bacteria to which oxygen is toxic)
which cause of this infection. These bacteria feed on
substances in the wood, releasing fatty acids, methane and
carbon dioxide gases. These fatty acids go rancid leaving the
wood of the tree water soaked and foul smelling.
The gaseous by-products create a hydraulic
pressure which forces liquids out of the cracks in the bark
which turns brown due to oxidization. The bacteria do not cause
any wood decay. However, the liquid raises the internal pH
(alkaline) causing the infected wood to resist decay for a few
years. Bark tissue will degrade in some cases.
Infection
is thought to enter the tree primarily through root uptake, but
contaminated pruning tools have all so been reported to transmit
this infection. Slime Flux wounds do not close properly as tree
tissue involved in wound closure are killed by the infection.
Control
There
is no satisfactory control for bacterial wetwood. It does cause
die back of branches, but as previously mentioned the raised pH
prevents and delays decay fungi from rotting out the heartwood
of the tree. Inserting drain tubes around the affected area is
no longer recommended. It only helps spread bacterial population
within and create wounds conductive to the entry of other
pathogens. As a radical effort and with some success with early
detection of one or two wounds using a hatchet to expose the
infection. Then spray the area with Ammonium Chloride, (Consan
20, a triple action microbial disinfectant), allowing the wound
to air dry as oxygen is also toxic to the bacteria. Preventative
measures such as avoiding moisture stress, proper pruning and
adequate fertilization may invigorate trees. Do not disturb soil
around the base of the tree to prevent wounds that the bacteria
may enter.
Also see
ASIAN AMBROSIA BEETLES
http://www.800oakwilt.com/asianambbeetles.html
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Scientists Find Sudden Oak Death Defense
By MIELIKKI ORG, Associated Press Writer
BERKELEY, Calif. - The secret to preventing the spread of sudden
oak death in coastal trees may be a gigantic booster shot.
University of California scientists have discovered that trees
dosed with a chemical product normally used as a fertilizer can
fight and even resist the deadly microbe that has killed more than
100,000 oaks throughout California and Oregon since 1995.
The new application, which was just approved by the California
Department of Pesticide Regulation, stimulates parts of the tree
that produce disease-fighting chemicals.
"It's not a cure, not a solution," said Matteo Garbelottoin, a
forest pathologist at the University of California at Berkeley who
discovered the effects of phosphite on infected trees in 2001. "But
we have something we can use to defend against the disease."
The chemical now is dispensed to the tree in two ways_ through a
syringe that puts the product directly into the tree's vascular
system, or through a spray that is absorbed through the bark.
Once the phosphite moves up the tree and enters the leaves, it
stimulates the production of infection-fighting chemicals within a
layer known as the cambium. The chemicals, although they do not
affect the pathogen, boost the tree's natural defenses.
At least 60 percent of the oak trees susceptible to sudden oak
death are on private coastal property, Garbelottoin said, which
means that homeowners may benefit most from the new treatment.
Arborists and foresters who use the phosphite product, which is
expected to cost about $30 per application, must be trained and
certified before they can use the chemical on private trees.
California's 16 state parks, where an estimated 4,000 acres of
oak trees show signs of sudden oak death, stand less to gain from
the new product.
"We have so much acreage, so many trees," said Richard Rayburn,
chief of natural resources at the California Department of Parks and
Recreation. "I'm not sure if we have the physical, or fiscal
ability."
United States Department of Agriculture officials said they plan
to continue placing quarantines on nurseries and other places in
California and Oregon where the pathogen has been known to spread.
Disclaimer:
This article may contain pesticide recommendations that are subject
to change at any time. These recommendations are provided only as a
guide. It is always the pesticide applicator’s responsibility, by
law, to read and follow all current label directions for the
specific pesticide being used. If any information in these
recommendations disagrees with the label, the recommendation must be
disregarded. No endorsement is intended for products mentioned, nor
is criticism meant for products not mentioned. The Writer assumes no
liability resulting from the use of these recommendations. The
information given herein is for educational purposes only. Reference
to commercial products or trade names is made with the understanding
that no discrimination is intended and no endorsement is implied.
Scenic Hills Nuirserry -
WARRANTY DISCLAIMER : http://www.scenichillsnursery.com/disclaimer.html
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