Cover Photo
Balsam fir foliage becomes tricolor after
several years of infection by needlecast fungi.
Introduction
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| Photo 1. Balsam fir needlecast disease in a Christmas tree plantation. |
Needlecast diseases are common in balsam fir
stands and Christmas tree plantations in the northeastern
and north central United States and in southern
Ontario, Quebec, and New Brunswick. Three
different needlecast fungi, Lirula nervata, Lirula mirabilis
and Isthmiella faullii, cause similar disease symptoms
on balsam fir. These diseases may affect other firs
planted in the same stand, but will not affect Douglas-fir or
other conifer species.
Injury from these pathogens ranges from
scattered brown needles to the loss of most of the three- and
four- year-old needles. Over a period of years, repeated
and severe needle damage can reduce tree growth, cause
bud and branch mortality on the lower portion of the
tree, and even kill small seedlings. This damage
decreases the quality of Christmas trees and makes
boughs unusable for wreath-making.
Biology and Symptoms
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| Photo 2. Single blister-like ridge of pycnidia of
Lirula nervata on upper surface of needle. The ridge is similar in color to the
needle prior to spore release, but darkens to
nearly black after spore release. |
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| Photo 3. Double ridge of pycnidia of Lirula
mirabilis on the upper surface of needles. The pycnidia remain similar
in color to the needle. |
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| Photo 4. Variable width and shape of ridge of pycnidia of
Isthmiella faullii on the upper surface of needles. The pycnidia
remain similar in color to the needle. |
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| Photo 5. Ascomata of L.nervata on underside
of balsam fir needles. They are nearly black in color. |
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| Photo 6. Closed (top) and open ascomata of
Lirula mirabilis on the underside of needles. |
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| Photo 7. Ascoma of Isthmiella faullii. It
appears very similar to Lirula mirabilis. |
The three needlecast fungi on balsam fir all have a
two-year life cycle and similar biology, including time
of infection and symptom expression. Annual infection
can result in distinctly tricolor foliage. The infected
current-year foliage remains green, showing no symptoms until
the following spring. The infected second-year foliage
is brown, and the infected third-year foliage bleaches to
a straw or tan color. Discolored needles may be shed or
be broken off in the third year, or they may remain
attached for a few years.
During the summer of the first year, fungal
ascospores (microscopic spores) infect the current year's needles.
Needles are infected individually and the fungus does
not spread into the adjacent needles or the twig. The
newly infected fir needles remain symptomless until the
following spring when they begin to discolor. Infected needles
then become pale and patchy green in color and slowly
turn brown as they die. Pycnidia (fungal
spore-producing structures) develop in the upper surface of these
brown needles in late spring of the second year and mature during summer.
They appear as pustules or as blister-like ridges.
The pycnidia vary in color, shape and placement
according to the specific fungus involved, and their appearance
can be used to distinguish among the three fungi (see photos
2-4).
Life cycle of Lirula nervata, typical of the needlecast fungi
on balsam fir.
The pycnidia produce tiny spores that are released
during and following periods of wet weather, but these
spores presumably do not infect fir needles.
In late summer of the second year, an ascoma (a
second type of spore producing structure,
pl., ascomata) begins to form on the midrib in the lower surface of the needle.
The ascoma will produce the infective spores called ascospores.
The infected needles discolor further to a pale tan or
straw color during the winter and spring months.
By the summer of the third year, the ascoma matures
and looks like a dark line along the lower midrib.
The darkness and width of the line vary slightly depending
on which fungus it is. When mature, a slit forms along
the length of the ascoma. During rain, the ascoma opens
along the slit and ascospores are released. Discolored
needles may be cast or broken off in the months
following ascospore release, or the faded grey needles may
remain attached for several years, but will not produce
spores again.
Life cycle of Lirula nervata, typical of the needlecast fungi on balsam fir.
Don't Confuse These With . . .
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| Photo 8. Small black pycnidia of R.
pini emerging from stomata of dead balsam fir needles. |
Many other fungi are often seen on balsam
fir needles. These fungi often thrive and proliferate under the
same moist, cool conditions as the needlecast fungi.
Rhizosphaera pini is a needle blight which differs
significantly from the needlecast fungi in its
fruiting structures, spores, and biology. Infected needles discolor
and often hang downward on balsam fir
branches.
Other fungi found on balsam fir needles may invade
dead or weakened foliage. Some of these fungi
effectively compete for foliar nutrients with the needlecast fungi
and thus may inhibit the completion of the needlecast life
cycle. The more commonly encountered balsam fir fungi
are shown in photos 9-13:
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|
Photo 9. Phaeocryptus nudus (arrow) on needle with
L. nervata. |
Photo 10. Lophodermium lacerum (arrows) on same
needle with (and inhibiting fruiting of) Lirula nervata. |
Photo 11. Stegopezizella balsamae. |
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| Photo 12. Leptosphaeria faullii (arrow) fruiting on needle
with old Lirula mirabilis pycnidia. |
Photo 13. Fir-fern needle rust,
Uredinopsis sp. |
Management
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| Photo 14. Needlecast disease on a forest-grown balsam fir seedling. |
Varying levels of needlecast may be observed in
forest grown stands and on intensively managed sites, such
as Christmas tree plantations. Most injury occurs on
small trees growing in cool, moist locations. Symptoms may
be observed one to three years following a wet
growing season. Damage is most evident on the lower
branches (within four or five feet of the ground), where
relative humidity is high and temperatures are lower. Disease
is most prevalent in low-lying areas, shaded areas and
areas where trees are crowded together. Areas where
young balsam fir are surrounded by tall fir can be an
ideal environment for high levels of disease. Young fir
trees near windbreaks and trees adjacent to densely
forested areas are commonly infected.
Control is usually not necessary because weather conditions and competition from other fungi keep
the damage below serious levels. In wild stands, some
disease may actually benefit the stand by serving to naturally
"thin" the weaker seedlings and reduce overcrowding.
However, in Christmas tree plantations, disease can cause
economic loss. The necessity for control will depend on the level
of disease which is present and the management objectives
for the stand.
Disease incidence (the number of individual trees
infected in your plantation) and disease
severity (the amount of living tissue affected by the plant pathogen) are
important pieces of information you will need to determine the
level of action necessary to manage these pests. Severity
can range from scattered tan needles to discoloration of
nearly all older needles and needle loss. The best time of year
to scout for this damage is winter and early spring.
The cultural management techniques listed below
should minimize disease. If you observe an increase in
the incidence or severity, consider more aggressive
disease management; contact your local forest health specialist
for the latest management recommendations.
Cultural Techniques in Christmas Tree Plantations
- Do not grow balsam fir in areas where cool moist
air collects and stagnates on a daily basis during
the growing season. Locate plantations in areas where
there is good air drainage.
- Carefully examine any native balsam fir for
infected needles before planting. Do not introduce these
diseases into your plantation by transplanting infected
native balsam fir.
- Do not interplant balsam fir in infected portions
of balsam fir plantations, as it tends to perpetuate
the disease in the stand.
- Provide adequate space between trees, prune off
lower branches and control weeds to allow more air flow.
- Do not leave live, infected branches on stumps
of harvested Christmas trees; they serve as
disease reservoirs.
- Shear healthy plantations first so disease spores will
not be carried into them from infected plantations.
- Do not shear infected foliage during wet
weather because spores released at this time may be carried
from tree to tree on shearing tools. Sterilize tools
after shearing infected plantations by dipping in
denatured alcohol for 3 minutes.
- If needlecast is a repeated and economic problem in
your plantation, grow a species other than balsam fir.
Diagnostic Characteristics
The following table describes the characteristics which
can be used by diagnosticians to distinguish among
needlecast diseases on balsam fir.
Photo 17. Cross section of needle showing asci in ascoma on
lower surface (arrow) and remains of pycnidia on upper surface.
| When and Where to Look |
Lirula nervata |
| By the summer of the second growing season, pycnidial
ridges have formed on the upper needle surface. |
The single, raised pycnidial line distinguishes this species
from the other two. It becomes black by late summer. The line may
be continuous or interrupted. Conidia are produced in
summer and are single-celled, hyaline, ovate, 4.5-6.0 x 1.0-1.2
µm. |
| By the summer of the third growing season, an ascoma
has formed on the lower needle midrib. |
The black ascoma commonly is continuous along the midrib.
Its width is 0.45 to 0.60 µm. Upon maturity the ascoma splits
open revealing the hymenial layer which is pale yellow.
Asci are cylindrical to clavate, 8-spored, 130-208 x
17-27µm. Paraphyses are filiform, almost straight, hyaline, 120 x 1.5
µm, sometimes branching and cutting spore-like cells.
Ascospores are filiform clavate, hyaline, 70-90 x 2.5-3.5
µm, and surrounded by a conspicuous gelatinous sheath 3-6
µm thick.
Photo 15. Ascus and ascospores.
Photo 16. Ascospore. |
| Lirula mirabilis |
Isthmiella faulii |
Pycnidia form in two raised lines, one on each wing of
needle. Pycnidial lines are the same color as the needle tissue
and may coalesce along the midrib. Conidia are produced in
the summer and are bacillar, hyaline, 2.4-3.0 x 7.0-9.0
µm. |
The heavy, labyrinthine or sinous pycnidial lines distinguish
this species from the other two. It may appear as a single line or
as two lines. The concolorous lines are variable in width.
Conidia are hyaline, elliptical, 3.0-3.5 x 1.0-1.2
µm, and are exuded in effused masses or tendrils. |
| The red-brown ascoma is continuous along the midrib.
Its width is 0.34 to 0.41 µm. The hymenial layer appears to
be pale yellow once the ascoma splits open.
Asci are broadly fusiform, 8-spored, 120-160 x 25-33
µm. Paraphyses are slender, filiform and about the same length
as the asci.
Photo 18. Ascus and ascospores.
Ascospores are cylindrical to clavate, tapering abruptly to
an acute base, 65-85 x 6-7 µm with a gelatinous sheath 5-6
µm thick. |
The dusky-brown ascoma is continuous along the midrib.
Its width is 0.20-0.30 µm. The hymenial layer is orange-buff
as the ascoma opens.
Asci are clavate, truncate at the tip when young, 8-spored,
85-135 x 16-25 µm. Paraphyses are filiform, straight, 125
µm x 1µm.
Photo 19. Ascus and ascospores.
Ascospores are double fusiform with slight constriction,
hyaline, 45-55 x 5-6 µm, surrounded by a gelatinous sheath 3-5
µm thick.
Photo 20. Ascospore.
|
References
Darker, Grant Dooks. 1932. The Hypodermataceae
of Conifers. Published by the Arnold Arboretum of Harvard University, Jamaica Plain, Massachusetts.
Darker, Grant Dooks. 1967. A Revision of the Genera
of the Hypodermataceae. Can. J. Bot. 45:1399-1444.
Funk, A. 1985. Foliar Fungi of Western Trees.
Published by Canadian Forestry Service, Victoria, B.C.
Albers, M., J. Albers, J. Cummings Carlson, L.
Haugen, and N. Wenner. 1996. Rhizosphaera Needle
Disease of Fir. USDA-FS Pest Alert, Pub. No. NA-PR-06-96.
Authors
Mike Albers, Forest Health
Specialist, Minnesota Department of Natural Resources, Grand
Rapids, Minnesota.
Jana Albers, Forest Health
Specialist, Minnesota Department of Natural Resources, Grand
Rapids, Minnesota.
Jane Cummings Carlson, Forest
Pathologist, Wisconsin Department of Natural
Resources, Madison, Wisconsin.
Linda Haugen, Plant Pathologist, USDA Forest
Service, Northeastern Area State and Private Forestry, St. Paul, Minnesota.
Nancy Wenner, Senior Research
Assistant, Department of Plant Pathology, Pennsylvania State
University, University Park, Pennsylvania.
Photo Credits:
Photo 1 by Jane Cummings Carlson
Photos 2, 3, 5, 6, 9, 15, 17, 18 by Linda Haugen
Photos 4, 7, 10, 11, 12, 13, 14, 16, 19, 20 and cover by Nancy Wenner
Photo 8 by Steve Katovich
This publication provides information on the
general biology of balsam fir needlecast diseases and
the characteristic features of diseased needles. Management recommendations to prevent
needlecast disease problems are presented.
As an aid to diagnosticians, microscopic characteristics of each of three common
needlecast fungi are presented in a table.
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