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Diplodia
shoot blight
damage (USFS). |
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Diplodia
canker on
the main stem (USFS). |
Shoot
blight and canker
diseases
In
the Lake States region, red pine
trees are often invaded by two
fungi that can kill shoots and
develop into cankers on larger
branches and main stems of trees. Diplodia
shoot blight and canker and Sirococcus
shoot blight are
two of the most important diseases
of red pine. They can be prevalent
on trees of all ages but the most
significant damage is generally
restricted to seedlings and saplings.
Both pathogens have unpredictable
outbreak patterns that are often
dictated by weather events. Diplodia
outbreaks tend to occur during
droughts or following hail storms,
while Sirococcus outbreaks often
occur following cool, wet spring
weather. During outbreaks many
seedlings and small trees can
be killed or deformed. Multi-cohort
red pine management, or growing
small red pine under larger red
pine, will increase the risk of
disease development. This is because
spores produced on infected large
trees are rain-splashed onto seedlings
and smaller trees growing below
them.
Diplodia
shoot blight and
canker (also
referred to as
Sphaeropsis) is
caused by the
fungus Diplodia
pinea.
The fungus causes
shoot blight on
large trees, shoot
blight and cankers
on sapling and
pole-sized trees,
and shoot blight
and collar rot
on seedlings.
Trees are infected
through succulent
shoot tissues,
branch stubs and
wounds. The fungus
can grow from
infected shoots
into branch and
stem wood where
cankers develop,
often girdling
and killing trees.
Diplodia
is often an episodic
disease, existing
at low levels for
years in some areas
without causing
significant injury
to trees. Some evidence
even indicates that
many trees carry
latent infections
that do not express
themselves until
a stress event occurs.
Weather can play
a major role in
the epidemiology
of this disease.
Epidemics are often
preceded by several
years of drought,
which stresses trees
making them susceptible
to Diplodia infection.
Epidemics are often
initiated locally
after hailstorms,
which create wounds
in branches and
stems that can be
quickly exploited
by the pathogen. This
type of scenario,
hail damage and
a Diplodia outbreak,
can destroy entire
plantations in 1
- 2 years.
Infected
reserve trees and
red pine windbreaks
are often the sources
of fungal inoculum.
Spores are released
from fruiting bodies
on infected bark,
needles and cones
during wet weather
and are disseminated
to adjacent trees.
Therefore, growing
small red pine
trees near larger
infected trees
is risky.
Planting
seedlings that were
infected in a nursery
but not displaying
disease symptoms
at the time of shipment
has likely contributed
to the widespread
occurrence of this
disease. The risk
of Diplodia can
be reduced by planting
healthy stock obtained
from nurseries known
to protect seedlings
from infection and
by not planting
or growing red pine
near infected trees.
Since this pathogen
is especially damaging
on stressed trees,
avoid planting red
pine on very dry,
nutrient poor sites.
These would be areas
where jack pine
would probably be
more appropriate.
Control of competing
vegetation to maintain
high tree vigor
can also reduce
disease impact.
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![[photo] Sirococcus shoot blight.](../images/scleroderris.jpg) |
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Sirococcus
shoot blight
damage. |
Sirococcus
shoot blight is
caused by the
fungus Sirococcus
conigenus.
Epidemics occur
periodically,
closely following
extended periods
of wet spring
weather. Damage
can be significant.
Young red pine
seedlings and
saplings can be
killed outright.
Many trees are
deformed by the
loss of shoots
and smaller branches.
Trees growing
under or adjacent
to infected red
pine can be severely
damaged when conditions
are optimum for
fungus dissemination
and development.
Sirococcus shoot
blight is most
likely to be a
problem in northern
parts of Wisconsin
and Minnesota
and in Michigan’s
Upper Peninsula.
Spores
are released in
spring and early
summer from fruiting
bodies that developed
on the previous
year’s
infected shoots.
The fungus infects
needles and grows
into current year’s
shoots. It is
not uncommon
to have trees
and individual
shoots infected
by both Sirococcus
and Diplodia,
collectively
increasing damage
and losses from
these diseases.
Similar
to Diplodia, outbreaks
of Sirococcus are
episodic and the
incidence and severity
of the disease can
rapidly increase.
Removing infected
overstory trees
and pruning infected
shoots on understory
trees before spore
dispersal in early
spring will reduce
the major sources
of inoculum and
minimize future
disease incidence.
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![[photo] Characteristic lower branch mortatlity due to scleroderris canker.](../images/scleroderris_canker.JPG) |
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Characteristic
lower branch
mortality due
to scleroderris
canker. |
Scleroderris
canker,
caused by the
fungus Gremmeniella
abietina,
is a disease most
serious on young
trees, seldom
causing damage
to trees taller
than 6 feet. The
disease develops
on lower branches
under snow cover
and the incidence
and severity of
the disease is
generally greatest
in frost pockets
and in areas where
deep snow accumulates.
Windblown
spores are disseminated
during wet weather
from April to October.
The spores infect
buds and needles.
Infected branch
tips are usually
dead by the following
summer. The fungus
can grow from the
branch into the
main stem where
a canker develops
that can girdle
and kill young trees.
The fungus produces
a second spore stage
that is disseminated
by rain splash from
killed branches
to adjacent trees,
increasing the disease
incidence.
Preventing
damage by Scleroderris
canker begins with
planting disease-free
nursery stock and
avoiding establishment
of plantings on
sites where Scleroderris
canker is present
or in frost pockets
and cold air drainages
where the disease
can become most
severe. Pruning
the lower branches
on infected and
healthy trees will
reduce disease incidence.
Shoot-
and tip-mining
insects
Shoot
and tip-mining insects cause damage
by affecting tree form and growth
rates. Over most of the range
of red pine, this group of insects
would not be considered a major
concern. However, there are two
moth species that do cause considerable
damage in some areas. The European
pine shoot moth occurs
in warmer parts of Lower Michigan
and the southeastern portions
of Wisconsin. The red
pine shoot moth is
prevalent in areas dominated by
outwash sands, such as the Central
Sands region of Wisconsin.
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![[photo] European pin shoot moth damage. (USFS).](../images/pineshootmoth.jpg) |
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European
pine shoot
moth damage
(USFS). |
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![[photo] Red pine shoot moth damage.](../images/redpineshootmoth.jpg) |
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Red
pine shoot moth
damage. |
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![[photo] Young tree dead in sweetfern](../../silv/img/sweetfern_tn.jpg) |
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Young
tree dead in
sweetfern. |
European
pine shoot moth, Rhyacionia
buoliana,
has been a pest
in Lower Michigan
since the 1950s.
Larvae feed on
buds and shoots.
Damage occurs
when a heavy infestation
destroys the buds
in the top whorl
of young trees,
creating twisted,
multi-stemmed
trees. Distribution
of this insect
is limited by
its inability
to survive cold
winter weather.
It can be found
in Lower Michigan,
southeastern Wisconsin,
and a few other
locations where
consistently heavy
snow cover provides
insulation for
winter survival.
Many trees attacked
and deformed when
young do, over
time, recover
and grow into
reasonably straight
trees.
Red
pine shoot moth, Dioryctria
resinosella,
was initially
identified as
a significant
pest in the 1980s
in the Central
Sands region of
Wisconsin. Larval
shoot feeding
resulted in height
growth losses
of 38-65% and
radial growth
losses of 16-42%
over a 9-year
epidemic period.
Following outbreaks,
tree crowns changed
from straight-stemmed
and conical to
a bushy and flat-topped
appearance. In
some plantations,
tree form was
altered enough
to make it difficult
to develop products
such as utility
poles and cabin
logs.
Management
of shoot and tip
moths can be difficult,
very little can
be done to limit
damage in the areas
susceptible to these
two insects. On
small trees, corrective
pruning may be useful,
especially on trees
that have their
terminal shoot damaged.
Sapsucking
insects
Sapsucking
insects can reduce tree health
or vigor by removing large quantities
of sap. But, what is more important,
their feeding often creates wounds
that eventually plug and permanently
reduce sap flow through twigs
and branches. Wound sites can
also serve as entry points for
pathogens. Sapsucking insects
include aphids, adelgids and spittlebugs.
Saratoga
spittlebug, Aphrophora
saratogensis,
has historically
been the most
significant insect
pest of young
red pine across
northern portions
of Michigan, Minnesota
and Wisconsin.
Outbreaks were
prevalent in the
1950s through
the early 1980s.
Adult Saratoga
spittlebugs insert
their straw-like
mouthparts into
red pine shoots.
Large spittlebug
populations cause
extensive wounding
that can kill
branches. Tree
mortality can
occur and plantation
failures have
been reported.
High populations
are associated
with abundant
sweetfern, the
plant that serves
as a host for
the immature stage
of the spittlebug.
Planting red pine
into areas where
sweetfern is abundant
creates a high
risk of spittlebug
attack. Several
other plants can
also serve as
an alternate host
including willows
and raspberries/blackberries.