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Pines
in the Midwest are susceptible to several needle blights and casts
that are caused by fungi that infect and kill (blight) the needles,
causing them to be shed or cast prematurely. The three most serious
blights and casts are Dothistroma needle blight (caused by
Dothistroma pini--also known as Scirrhia pini in its sexual
stage), brown spot needle blight (caused by Scirrhia acicola),
and Lophodermium needle cast (caused by Lophodermium seditiosum).
Two blights that are usually less widespread and serious are Jack
pine needle blight (caused by Davisomycella ampla and
affecting mainly Pinus banksiana) and needle blight of
pine (caused by Meloderma desmazierii, a weak parasite
that rarely causes notable loss of needles). Table 1 lists the species
of pine more commonly grown in the Midwest that are susceptible
to these diseases.
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Infection
characteristically first occurs in the older, lower branches
and works upward in successive years (Figure 1). When infection
is severe, limbs over the entire tree can be infected. Repeated
premature loss of needles not only disfigures a tree but can
seriously reduce its vigor. Continued annual infection by
one or more needle blights and casts can eventually kill even
older trees. Disease epidemics of pines growing in windbreaks,
ornamentals plantings, or nurseries have led to considerable
economic losses. These needle diseases appear to be most damaging
on highly susceptible strains of Scots pine grown for Christmas
trees or on trees that are in poor vigor because of some site-related
factor, insect injury, or other disease.
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Click
on image for larger version
Figure 1. Scots Pines in a Christmas Tree Nursery with
Characteristic Defoliation by Lophodermium Needle Cast Beginning
on Lower Branches (Dr. D.H. Scott, Purdue University)
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Click
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Figure 2. Dothistroma Needle Blight or Red Band Disease
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Symptoms
Symptoms of these diseases are quite similar. In all case,
fungi cause spotting or banding of the needles (Figures 2-4).
As infection progresses, these areas gradually enlarge and
merge, with the entire needle dying and turning brown or reddish
brown, usually from the tip back. Depending on the fungus,
infection may involve only current-season needles, only old
needles, or both.
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Dothistroma
Needle Blight or Red Band Disease
(Dothistroma pini; Scirrhia pini is the perfect or
sexual stage). During autumn and early winter, circular to oblong,
water-soaked spots appear on needles of all ages. The spots become
yellow to tan, then brown to reddish brown, and may develop into
reddish bands that gradually girdle the needle (Figure 2). The tip
end of the needle turns brown while the base remains green. The
dead tip may break off, leaving a short, blunt needle. As the blight
progresses, the bases of the needles also die. Typically, clusters
of needles on a shoot are uniformly infected.
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Table
1. Species of Pine Commonly Grown in the Midwest That
are Susceptible to Needle Blight and Needle Cast Diseases
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Disease
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Species
of pine (Pinus) affected
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Dothistroma
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Austrian
(P. Nigra), ponderosa (P. ponderosa) and Mugo
(P. mugo) needle blight are the most severely affected.
Other susceptible pines include red (P. resinosa) and
Scots (P. sylvestris).
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Brown
spot
needle blight
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Most
severely affected are the short needle varieties of Scots
pine (P. sylvestris) such as Spanish and French Green. Other
susceptible pines are Austrian (P. nigra), eastern white (P.
strobus), and ponderosa (P. ponderosa).
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Lophodermium
needle cast
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Scots
(P. sylvestris) and red (P. resinosa) are the
two species most seriously affected. Short needle varieties
of Scots pine (such as Spanish and French Green) are highly
susceptible; long needle varieties, such as Scottish Highland
and Austrian Hills, have greater resistance. Ponderosa (P.
ponderosa) and Austrian (P. nigra) pines are also
susceptible.
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Jack
pine
needle blight
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Jack
pine (P. banksiana) can be severely defoliated. Eastern white
(P. Strobus is susceptible but less commonly infected.
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Needle
blight
of pine
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Jack
(P. banksiana), limber (P. flexilis), Austrian
(P. nigra), red (P. resinosa), eastern white
(P. strobus), and Scots (P. sylvestris) pines
are susceptible. The reddish tint and the banding of the needles
are most distinctive and numerous on infected pines in the
Pacific Northwest where the disease is often referred to as
the red band disease.
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Infected
needles drop prematurely, and usually infected second-year needles
are cast before the current-season needles, sometimes in late fall
of the year they became infected. However, spring and summer are
usually the periods of greatest needle loss. Blighted first-year
needles often are not shed until the summer following the year they
were infected.
Infection
is usually worse on the lower half of the tree, but in severe cases
the entire tree may be uniformly infected. In early spring, black
fruiting bodies (pycnidia and ascocarps) erupt through the epidermis
of infected needles. These bodies may, however, appear as early
as the autumn of the year of infection.
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Brown
Spot Needle Blight
(Scirrhia acicola; imperfect stage is Lecanosticta
acicola). In August and September, small gray-green to
gray-black spots appear on the current-season needles. The
spots later turn brown with yellow halos. They enlarge and
may merge to form irregular, oblong areas. Often they are
covered with pitch (Figure 3). Several weeks after the appearance
of the spots, the infected needles begin to die back from
the tips. By October and November, entire needles turn brown
or orange-red, as if killed by fire, and many fall off. Some,
however, remain on the tree until the following summer.
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Click
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Figure 3. Brown Spot Needle Blight on Red Pine
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Defoliation
is most conspicuous on the lower branches, and particularly on the
north side of infected trees. In late summer, small black fruiting
bodies (pycnidia and ascocarps) form on the dead needles, both those
on the tree and on the ground. Unlike the fruiting bodies of the
Lophodermium needle cast fungus, these are not football-shaped,
but are more oval. Also, the fruiting bodies protrude only slightly
from the needle surface when wet. When dry, they are flush with
the needle surface.
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Click
on image for larger version
Figure 4. Lophodermium Needle Cast on Dead Pine Needles
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Lophpdermium
Needle Cast
(Lophodermium seditiosum; most reports dealing with
outbreaks of L. pinastri almost invariably concern
L. seditiosum). In late March or April, small brown
spots with yellow halos appear on last year's needles. The
spots enlarge, the entire needle begins to turn yellow, and
by late spring it is brown. The dead needles are shed in early
summer and throughout the growing season. In severe cases,
most of the foliage of the previous year is shed by autumn,
leaving only tufts of green, current-season needles at the
tips of branches. Infection is usually worse on the lower
half of the tree. When severe, the entire tree may be uniformly
infected (Figure 1).
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In
late summer, small black, football-shaped fruiting bodies (pycnidia
and ascocarps) appear as conspicuous protrusions (particularly when
wet) on the dead needles. The bodies have a characteristic lengthwise
slit down their center. Sometimes, diffuse brown lines running across
the needle appear with the fruiting bodies. These lines are characteristic
of infection by Lophodermium.
Jack
Pine Needle Blight
(Davisomycella ampla; synonyms Lophodermium pinastri
and Hypodermella ampla). One- and two-year-old needles become
yellow, then brown, and are shed, leaving only the current-season's
foliage on the twigs. Dark gray to black fruiting bodies (pycnidia
and ascocarps) appear on the dead tips of the needles.
Needle
Blight of Pines
(Meloderma desmazierii). Yellow spots appear on the needles
in early spring from the previous year's infection. These spots
turn brown and enlarge, giving severely infected trees a reddish
tinge. Black fruiting bodies (ascocarps) appear at the tips of dead
needles in February and ripen from May to July. Spores are spread
during the summer and needles become infected. The yellow spotting,
however, does not develop until the following spring. The characteristic
formation of fruiting bodies at the tips of the dead needles is
one way to distinguish this needle blight from that caused by Lophodermium
seditiosum.
Disease
Cycle
Two types of microscopic spores (conidia and ascospores) are produced
in the fungal fruiting bodies (pycnidia and ascocarps) that develop
beneath the epidermis of the needles. (The fruiting bodies can be
seen easily with a 10X hand lens). When mature, the fruiting bodies
erupt through the epidermis. Spores are released during rainy periods
and infect healthy needles, usually through the stomates. Transmission
is by air for Lophodermium needle cast spores and by splashing rain
for Dothistroma and brown spot needle blights. The fungus mycelium
then colonizes the tissues of the needle. In some instances, death
of the needle does not occur until the growing season following
the year of infection, and fruiting bodies do not mature until the.
In other cases, death and the formation of fruiting bodies occurs
in the fall of the year of infection.
Dothistroma
Needle Blight
The
fungus overwinters as fruiting bodies (pycnidia and ascocarps) on
dead needles infected during the previous growing season. In late
March the fruiting bodies enlarge, and by mid-May they mature and
erupt through the needle epidermis. Microscopic spores (conidia
and ascospores) are shed during rainy periods from mid-May to October,
infecting second-year and older needles. Current-season needles
do not become susceptible to infection until midsummer. The spores
are transported short distances by splashing rain; few spores become
truly airborne. Under special conditions, clouds may carry spores
over long distances.
Germinating
spores enter the needles through the stomates, and considerable
growth of the fungus takes place in the stomatal pit before the
internal tissues are penetrated. The minimum, optimum, and maximum
temperatures for spore germination and mycelial growth are approximately
41, 64, and 77°F (5, 18, and 25°C), respectively. The
period from spore infection to development of symptoms is six to
twelve weeks, depending on environmental and host conditions. Fruiting
bodies develop below the epidermis in the dead parts of the needles
soon after they die. The fruiting bodies may enlarge sufficiently
in the fall to split the epidermis, but generally they do not mature
and produce spores until the following spring.
Brown
Spot Needle Blight
The Scirrhia fungus overwinters as fruiting bodies (ascocarps
and pycnidia) in dead needles or parts of infected needles, or as
vegetative mycelium in infected needles. In the spring, microscopic
spores (conidia) are discharged during wet weather, and spore production
increases until late summer. Spore transport is by splashing rain.
Spores infect current-season needles, and the fungus mycelium colonizes
the needle, eventually killing it by the end of the summer. The
fungus spreads internally through the nonspotted parts of the needle,
particularly during the following March and April. By mid or late
summer the entire needle dies and fruiting bodies develop in the
epidermis.
Lophpdermium
Needle Cast
The Lophodermium fungus overwinters as vegetative mycelium
in needles infected the previous season. Fruiting bodies (ascocarps
and pycnidia) develop during early summer, maturing by late summer.
Spore discharge occurs from late summer to mid-fall. Spore transmission
is by air currents. Spores germinate and infect the current-season
needles. The pathogen remains as vegetative mycelium in the leaf
tissue during the winter.
Jack
Pine Needle Blight
Very little is known concerning the disease cycle of the Davisomycella
fungus.
Needle
Blight of Pines
Very little is known concerning the disease cycle. The Meloderma
fungus is generally considered to be a weak parasite.
Control
- Transplant
only healthy nursery stock.
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Maintain tree vigor by watering during droughts and fertilizing
in fall or early spring based on a soil test report. Space plants
to avoid crowding, and promote good air circulation around trees.
Do not allow weeds or tall grass to grow up around the lower branches.
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Destroy and burn or compost infected seedlings whenever feasible.
Detection of Dothistroma needle blight is often difficult because
the level of infection may be low and the symptoms do not develop
until late summer.
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Where possible, avoid: 1) establishing pine seed beds adjacent
to older pines in the nursery, and 2) placing pine lining-out
stock next to older pines in the nursery.
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Carefully check pines in windbreaks and landscape plantings on
the nursery grounds for evidence of needle blights and casts.
If infected, they should be sprayed (see No. 9 below).
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Identify disease early to minimize losses. Using the information
given in the disease cycles outlined above, and the figures, check
the pines at appropriate times when symptoms are expected to appear.
Make plans for a spray program where this is feasible (see No.
9 below).
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Shear healthy trees before infected trees. Pruning tools should
be sterilized between trees by dipping in denatured alcohol (rubbing
alcohol) for three minutes. Avoid shearing infected trees when
the foliage is wet.
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Avoid planting pine species and varieties that are highly susceptible
(Table 1).
- A suggested spray program to control needle blights and casts
is given in Illinois Urban Pest Management Handbook, which
is revised annually. When mixing and applying fungicides, it is
important to apply a suggested chemical at the right time, using
sufficient pressure to get uniform coverage of the needles. The
manufacturer's directions and precautions on the container label
should be carefully followed.
For
further information concerning diseases of woody ornamentals, contact
Nancy R. Pataky, Extension Specialist and Director of the Plant
Disease Clinic, Department of Crop Sciences, University of Illinois
at Urbana.
University
of Illinois Extension provides equal opportunities in programs and
employment.
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