VASCULAR WILT DISEASES

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VASCULAR WILT DISEASES Text Chapter 14
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Three Important Vascular Wilt Diseases 1. Oak
wilt caused by Ceratocystis fagacearum 2.
Verticillium wilt caused by Verticillium
dahliae and V. albo-atrum 3. Dutch elm disease
caused by Ophiostoma ulmi and O.
nova-ulmi These diseases are mostly a problem in
urban areas and urban forests, but oak wilt is a
problem in forests.
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OAK WILT
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Oak wilt is one of the most serious tree diseases
in the eastern United States, killing thousands
of oaks each year in forests, woodlots, and home
landscapes. Oak wilt was first identified in
1944. The fungal pathogen that causes the
disease, Ceratocystis fagacearum, is thought by
most to be native to the eastern United States,
but difficulty in isolating and identifying the
fungus delayed recognition of the extent of its
impact until the 1980's. Some plant pathologists
think that oak wilt is an exotic disease,
arriving in North America in the early 1900's,
but the fungus has never been reported from any
country other than the United States. The disease
has also become much more apparent in some local
areas since the 1980's because of increased tree
wounding, due primarily to home construction in
oak woods.
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Life cycle of oak wilt fungus
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Dead oak in Austin, TX
Distribution of oak wilt in 1988 (red)
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Oak Wilt Management Buffer
zone/trenching Sanitation remove infected
material Pruning treat pruning tools with
clorox Wound paint on pruning cuts and
wounds Careful with firewood Chemical stem
injection ALAMO Replanting
with non susceptible hosts
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VERTICILLIUM WILT
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Verticillium Wilt
Hosts Some of the many common woody ornamental
host plants include ash, barberry, catalpa, elm,
magnolia, maple, Russian olive, redbud,
smoketree, tuliptree, and viburnum. One group of
plants not susceptible to Verticillium wilt are
all the gymnosperms, including conifers such as
pine and spruce. While many landscape plants are
affected, Verticillium wilt is not a major
problem in natural forested areas.
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The fungus enters a tree by way of its roots and
spreads from there through the sapwood into the
upper branches. One or more large limbs or even
the entire crown may begin to die back. Sometimes
leaves will have marginal browning or scorch
symptoms. Survival time depends on the size and
vigor of the tree, as well as general weather
conditions. Olive-green streaks sometimes can be
seen in the sapwood. Usually they will be some
distance below the place where the leaves are
wilted or scorched.
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MANAGEMENT Once the
disease becomes established, it's hard to
control. - cut down and destroy seriously
infected trees. - pruning out the infected
branches, - giving the tree a generous feeding,
and watering during dry periods. - Feed in the
early spring at bud swell with a 10-6-4,
10-10-10 or other high-nitrogen fertilizer.
Supplement this in late spring and early summer
with applications of a soluble fertilizer to
stimulate leaf growth.
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DUTCH ELM DISEASE
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Elm
facts Elms provide food, medicine, fodder,
shelter, tools, boats, plows, weapons,
furniture, shade, and ornamental and recreational
value 136 million landscape elms gt 10 cm diam on
all 6 continents - 95 in Europe N. America and
Asia 1976 - 30 million in U.S. worth billions
of dollars 40 million died from DED 32 species
of elms - American (U. americana) and English
(U. procera) largest species Large trees - can
live for 500 yrs, gt 100 ft in height, 13ft in
diam, 147 feet in branch spread.
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Can tolerate both wet and dry conditions
make excellent street trees. Can endure physical
damage and tolerate a variety of soils Nightmare
on elm street has nothing to do with elms
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Dead elm street trees
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Spread mechanisms 1. Via bark
beetles and spore infection in branches and
boles 2. Via mycelium through root grafts
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Vectors of Dutch Elm Disease Fungi European
elm bark beetle - Scolytus multistriatus (Great
Britain, southern Europe to Sweden,United States,
southern Canada (introduced), Australia
(introduced), New Zealand (introduced) - attacks
branchs Native elm bark beetle - Hylurgopinus
rufipes (primary vector in northern U.S, New
England and Canada) - attacks boles and
branches 15 other beetle species
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The pathogen - probably originally from
Asia Ophiostoma ulmi Ophiostoma
nova-ulmi 1918 - identified in the
Netherlands 1930 - Ohio 1933 - New York City 1950
- Canada 1960 - U.K. (O. nova-ulmi) 1977 -
Washington 2001 - Seattle
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Control Non-Chemical Control Use of resistant
varieties Sanitation Pruning Therapy -
disease arrest, pathogen excision (surgery),
other organisms (Dutch Trig) Mass
trapping of Elm bark beetles Chemical Control
Fungicide Injection, insecticides
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Resistant Varieties Valley
Forge New Harmony Prospector Patriot
Accolade Have high levels of tolerance, but not
immune Asian elms have high resistance
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Sanitation 1. Systematic surveys for early
detection 2. Felling and destroying trees
promptly after infection 3. Pruning declining
branches that attract beetle vectors 4.
Destroying all elm fuel wood by early spring 5.
Debarking and drying wood 6. Immersing wood in
water for long periods 7. Poisoning cut wood with
insecticides 8. Treating live trees with
herbicides/or insecticides 9. Trapping insect
vectors by logs or pheromones 10. Immediate
burning or deep burying of elm wood
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Non-fungicide protective treatment
Dutch Trig A
suspension of live spores of the fungus
Verticillium dahliae injected into the tree by
gouge pistol. Protects by inducing resistance in
the tree Pros Small injection holes, rapid,
less costly than fungicide Cons Must be applied
every year V. dahliae is a plant pathogen Only an
option before infection
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Fungicide
injection Microinjection - forceful injection of
a low volume of concentrated chemical into
holes drilled into the stem or base of
tree Macroinjection - injection (under
pressure) or infusion (without pressure) of a
large volume of dilute chemicals solutions in
the stem or base of tree.
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Available
chemicals Benzimidazole compounds - systemic
and active at low concentrations
(Carbendazim phosphate, thiabendazole
hypophosphite, and Decacarb) Triazole compounds
(propiconazole, tebuconazole) Copper sulphate
pentahydrate
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