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LAMINATED
ROOT ROT, YELLOW RING ROT
(Phellinus (Poria) weirii)
Hosts:
Most conifers
Highly susceptible: Douglas-fir, mountain hemlock, western
hemlock, grand and Pacific silver fir
Moderately susceptible: spruces, larch, noble and subalpine
fir, western redcedar
Tolerant: lodgepole pine, western white pine
Resistant: ponderosa pine
Immune: Hardwoods
Quick ID:
- Crown yellowing
and thinning
- Distress
crop of cones, especially in Douglas-fir
- Frequent
windthrow with "root balls"
- Buff colored
mycelia may occur on the outside of roots.
- Outer heartwood
stained red-brown
- Annual rings
separate
- Reddish
brown fungal hairs between sheets of decayed wood (use hand lens
to identify)
- Affected
trees often in groups or patches
 Field
Identification
Tree &
Stand: Affected trees show marked reduction in height and diameter
growth. The crown thins and yellows, and may frequently produce
a distress crop of cones. Trees are commonly windthrown after the
disease rots off roots just below the root collar, forming a "root
ball." Early in the decay process, crescent-shaped or semicircular
reddish brown staining of the wood may be observed. As decay progresses,
the wood softens. The earlywood disintegrates more quickly than
the latewood in each annual ring, resulting in a laminated ring
rot where the annual rings of the wood separate. Small oval pits
appear on both sides of the separated wood sheets. This disease
forms root rot centers, where the disease has spread out over time
from an initial infection. In the center will be either an old stump
or an empty area, or in an old center, regeneration. Trees within
several yards to hundreds of feet (depending on the size and age
of the infection) will be dead or dying, and trees further out will
show early crown symptoms. Trees within 50 feet of the apparent
edge of a disease center are very probably infected as well, but
will not show crown symptoms until half to 75% of the roots are
infected. Root rot centers may be many acres in size, and spread
out at the rate of about 1-2 feet per year.
Fungus:
Fruiting bodies (conks) are uncommon, but when found are located
in protected areas such as on upturned roots and on the underside
of decayed logs. Conks are flattened and range in color from buff
to dark brown, with a white margin. The exposed surface is covered
with many small pores. Reddish brown to brown whiskery mycelia (fungal
fibers) may be observed between sheets of decayed wood, and white
to purple-grey mycelial sheaths may be observed on outer bark surface
of roots.
May be confused
with: Armillaria root rot, Annosus root and butt rot, or animal
damage.
Disease
cycle: Laminated root rot is considered to be the most damaging
root disease in the Pacific Northwest, as it kills the greatest
concentrations of trees in the areas where it is present. There
appears to be two distinct forms, one that causes a root disease
in Douglas-fir, grand fir, and hemlock, and another form that causes
a butt rot of western redcedar. The western redcedar form has only
been identified on the east side of the Cascades, although western
redcedar on the west side occasionally becomes infected with the
Douglas-fir form, to which it is tolerant. The disease is spread
by root contact between a healthy and infected individual. Mycelia
of the fungus
do not grow through the soil, nor are windblown spores a major factor
in disease spread. The fungus may remain viable in stumps for 50
years and thus infect regeneration, although it typically takes
10 to 15 years for root contact with the new trees to be established.
The disease kills susceptible hosts by either predisposing them
to windthrow by rotting the major roots, or by destroying their
ability to take up water and nutrients. Saplings and small poles
are usually killed quickly, while older trees may confine the fungus
to a small number of roots or to the butt log and survive for many
years. Trees of intermediate susceptibility are often infected but
rarely killed,
while tolerant species are seldom infected and almost never killed.
Predisposing
agents: Although all conifer species can be infected by laminated
root rot, susceptibility varies. Old infected stumps from previously
infected stands are a serious problem for regeneration of highly
susceptible species. Certain silvicultural procedures such as commercial
thinning or uneven-aged management may make infestations worse.
The disease often occurs with other root diseases such as Armillaria
root rot or Annosus root and butt rot. Laminated root rot is itself
a predisposing agent for bark beetle attack.
Impact:
On the west side of Oregon and Washington, laminated root rot causes
annual losses of 32 million cubic feet of wood; east side damages
could be equally high. The incidence of the disease has probably
increased substantially with the suppression of fire and subsequent
species shift to Douglas-fir/grand fir forests, as these species
are highly susceptible to laminated root rot; ponderosa pine and
western larch are more tolerant.
Management:
Laminated root rot often occurs with other root diseases and predisposes
trees to bark beetle attack. Always check apparent bark beetle kills
for root disease signs as their presence may influence species regeneration
and silvicultural methods. Control of laminated root rot is best
attempted at the time of final harvest. Prior to harvest, the disease
centers should be marked by examining outlying trees for characteristics
of the disease (e.g. mycelia on the roots, reddish stain in the
heartwood). Infected trees should be marked low on the bole so the
mark remains after harvest. It is suggested that disease centers
should be mapped as well as marked to enable them to be tracked
over time. Global Positioning Systems (GPS) may make mapping centers
and tracking them over time easier, and that technology is rapidly
becoming affordable. All trees in the disease center, as well as
uninfected trees within 50 feet, should be cut. During the harvest,
stumps should be examined outside the marked disease center for
the characteristic red-brown semicircular staining; the disease
center boundaries and buffer strips should be adjusted accordingly.
It is important to check within a day or two of harvest as the stain
fades quickly upon exposure to air. In Washington, the easiest,
most cost-effective control is replacement of Douglas-fir/grand
fir stands with other, less susceptible species. One 50-year rotation
of tolerant, resistant or immune species such as ponderosa pine,
western white pine, lodgepole pine, or western redcedar should result
in the disease dying out on the site, provided that susceptible
trees are not permitted to be reestablished. Another good alternative
is a hardwood species such as alder, which is immune to the disease.
A rotation of an intermediately susceptible species such as western
larch may permit laminated root rot to remain on the site, though
at a lower level than with highly susceptible species. Interplanting
highly or intermediately susceptible trees with tolerant or rsistant
trees will not help them survive; on the contrary, it is more probable
that the tolerant trees will become infected. Susceptible species
should not be planted within 100 feet of a disease
center. Another alternative is to treat inoculum by removing as
many infected roots and stumps as possible. A bulldozer or excavator
may be used to push out stumps or push over whole trees; on some
sites explosives could be appropriate. Uprooted roots and stumps
need not be burned as air drying kills the fungus.
In 10 to 15-year-old
sapling stands with less than 25% of the area infected, thinning
the diseased trees could be an effective measure. In young stands
affected trees will appear scattered rather than in clear disease
centers. All trees displaying symptoms, as well as all those adjacent
to them (within two normal tree spacings, both high and intermediate
in susceptibility), should be cut. This should break the disease
pathway to healthy trees by killing the roots on which the disease
spreads. It is important to cut the adjacent trees that do not
show symptoms as the disease may be in an early stage and thus
undetectable, or the tree may become infected later as its roots
grow towards the disease center. When precommercially thinning near
disease centers, always try to save tolerant or less susceptible
species. Silvicultural treatments such as weed control or fertilization
to maximize growth will neither help nor hinder the spread of the
disease. Heavily infected sapling stands may be grown to harvestable
small poles before losses become severe.
Where pole
stands have numerous disease centers and more than 20% of the area
is visibly affected, do not commercially thin; harvest at a younger
rotation age. In pole stands which do not have numerous centers,
or in which the centers are widely distributed, infected trees and
nonsymptomatic adjacent trees should be harvested in a commercial
thinning. The stand should be monitored for windthrown trees, which
should be removed yearly to prevent their infestation by bark beetles.
Adapted from
Hadfield, J.S. and D.W. Johnson, Laminated Root Rot. USDA Forest
Service -Pacific Northwest Region, 1977, and from Hadfield, J.S.
et al., Root Diseases in Oregon and Washington Conifers, USDA Forest
Service-Pacific Northwest Region, 1986.
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