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* uw's david zuckerman on adelgid predators (8 apr 2013)
Hi-
Some very interesting info & always good to learn how nature balances itself:
Hello Cheryl,
There are 2 natural predators of the adelgid that typically are
present in our hemlocks. The more prevalent ‘winter predator’ is a
tiny shiny black beetle related to the ladybug, known as Laricobius
nigrinus and a ‘summer predator’ another beetle w/ a golden hue known
as Scymnus coniferarum. Both beetles occur together in the
winter. It's a fascinating story of discovery and conservation. The
eastern hemlock forests have been decimated by the
adelgid. Researchers wondered why our western hemlocks were not
succumbing to the adelgid since it was observed that most of them had
it. There’s a fascinating back story about spending lots of research $
and time scouring the forests of Asia for biologic controls for the
adelgid, when all along our western hemlocks held the answer. Once the
beetles were discovered in our hemlocks, massive efforts were made to
harvest these predators, rear them in laboratories and release them
into the eastern hemlock forests. There are now a few areas back east
that are supporting the predators and the hemlocks in these areas are
slowly reaching a state of sustainability w/ the adelgid.
Now having said all this and knowing that our hemlocks rarely, if
ever, succumb soley due to the presence of the adelgid, there is
probably something else going on w/ your tree that you may or may not
be aware of. There’s a general rule of thumb that most insect pests
are secondary and don’t come in unless there are other stressors,
e.g. climate changes from drought or flooding, grade changes or other
construction impacts, etc.
I would recommend you hire a consulting arborist to inspect your tree
and determine what could be causing its decline. I do not recommend
spraying your hemlock for the adelgid until all else has been
eliminated as the primary cause of your tree’s decline.
Good luck!
David Zuckerman
Manager of Horticulture and Plant Records
UW Botanic Gardens
VM 206.543.8008
FX 206.616.2971
dzman@uw.edu
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* for erica howard, cornish science teacher, for centennial exhibit (apr 2011)
Annosus root and butt rot (Heterobasidion annosum) is a native disease that spreads by airborne spores and enters through
wounds in the stem or roots. Neighboring hemlock trees can root graft, so the disease can subsequently spread by through the roots from one tree to
another, resulting in what foresters sometimes call a "ring of death". There is no known cure cure for the disease once trees are infected.
Keeping them healthy and not wounded is obviously important.
Hemlocks are quite abundant in the northern half of Seward Park's old growth forest. We find a modest number of
dead snags, and a few worrisome tight clusters of dead trees. The latter appear to be caused by annosus infestation.
Our initial concern that annosus was spreading quickly has not been borne out by measurements we have made, the results
of which are illustrated in the attached map.
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* annosus
Heterobasidion annosum (formerly Fomes annosus) is a plant pathogen and a Basidiomycete fungus
that causes root and butt rot to conifers. It establishes in wounds or stump surfaces created by
tree felling. The mycelium grows through root systems and infects helthy trees at points of root
contacts or root grafts. Annosum root rot of conifers causes major economic losses to forestry,
more than 580 million euro annually in western Europe alone.
[http://www.pfc.cfs.nrcan.gc.ca/pathology/rootd/annosus_e.html]
...is endemic in many temperate zone forests, where it causes mortality and butt rot of
conifers. Two varieties of the fungus occur in western North America, the spruce and pine
types. Only the spruce type has been detected in British Columbia. In British Columbia, studies
have shown that the range of H. annosum is approximately coincident with that of western
hemlock. Within its range, the fungus has been found on all commercially important conifer species
and on alder and broadleaf maple.
In old growth forests, H. annosum causes butt rot. In second growth, trees whose roots contact
H. annosum inoculum in old-growth stumps may be killed when less than 15 years old, windthrown
when roots are decayed, or butt-rotted. The incidence of Annosus root disease and the damage it
causes in managed forests are related to the frequency and intensity of thinnings. The fungus
infects freshly cut stumps by means of airborne spores, and may colonize the stump, grow into its
roots, and spread to adjacent healthy trees at root contacts. Airborne spores also infect stem
wounds on thin-barked species such as hemlock and fir (Abies spp.); extensive decay can develop
above and below the wound.
Root and butt rot and decay associated with stem wounds are commonly seen throughout the range of
Heterobasidion annosum. In old growth forests, the incidence of H. annosum can be as high as 5%
(mean 1.5%) in western hemlock, amabilis fir, western redcedar, Sitka spruce, Douglas-fir, and
subalpine fir. However, the volume of decay attributed to H. annosum in these stands may be small,
especially compared to volumes of decay caused by true heartrot fungi such as Phellinus pini and
Echinodontium tinctorium. In unthinned second-growth stands, up to 5% of trees may have butt rot
caused by H. annosum, with disease centers containing up to five trees in Douglas-fir plantations,
and up to 20 trees in hemlock stands.
Studies of tree wounds indicate that about one-half of wounds larger than 1000 square centimetres
on the lower bole of second-growth hemlock can be colonized by H. annosum and the fungus can decay
0.5-0.7% of the tree's volume annually. Results of thinning studies show that up to 20% of Sitka
spruce and amabilis fir stumps in precommercial thinnings may be colonized by H. annosum, compared
to 6% and 10% of Douglas-fir and hemlock stumps, respectively. The incidence of stumps colonized
by H annosum varies with stump diameter, season of thinning, stand age and biogeoclimatic subzone.
Young trees that have most of their roots killed by the fungus usually exhibit typical symptoms of
root disease, including reduced leader growth, faded foliage, and distress cones. In older trees
the fungus causes butt rot, and external symptoms are not evident. Trees with extensive decay in
their roots are susceptible to windthrow and one or more windthrown trees may indicate the
presence of an Annosus root disease center, especially in hemlock stands. Fruiting bodies (conks)
of the fungus are produced on colonized stumps and on the decayed exposed roots and the underside
of the stem of windthrown trees. The early stage of H. annosum decay is a yellow-brown to
red-brown stain, while in advanced stages the wood is reduced to a white stringy mass containing
black flecks running parallel to the grain. A useful test to confirm the fungus in a wood sample
is to wrap it in moist paper, enclose it in a plastic bag and store it at room temperature. After
7 days, the asexual fruiting structures of the fungus will form on the wood surface.
--- wsu: http://ext.nrs.wsu.edu/forestryext/foresthealth/notes/annosusrootdisease.htm
The most obvious sign of Annosus root rot is the fruiting body (conk), found inside old stumps or
in the duff layer on the exterior of roots and root collars of infected or dead trees. The conk
may take several forms. Small, button-like conks may be found on the wood beneath the bark of
pine stumps and on the surface of small pine roots in the soil. On the root collar of infected
trees, conks ranging from 1/2 to 2" in size may be found under the litter layer. Inside rotted
stumps or on the underside of exposed roots of windthrown trees, conks tend to be large (up to
10" wide) and irregularly shaped. The conks, which are perennial, have a dark upper surface and a
creamy white lower surface covered with tiny pores.
May be confused with: Laminated root rot, Armillaria root rot.
Disease cycle: Annosus root rot is considered third in severity in the Pacific Northwest, after
laminated root rot and Armillaria root rot. Researchers have identified at least two
host-specific forms of the disease: an s-type that infects mostly spruce, firs, Douglas-fir,
western redcedar, and hemlock, and a p-type that occurs mainly on pines but will infect the same
species as the s-type, as well as brush and hardwood species. Unlike laminated or Armillaria root
rot, Annosus spreads both by root contact and by spore infection. When the roots of a healthy
individual touch the roots of a diseased individual, a new infection results. As well, windborne
spores that are deposited on freshly-cut wood surfaces such as stumps or basal wounds germinate
and infect the surface.
Annosus can live for 50 years in large stumps of resinous trees; in smaller stumps and
nonresinous species survival time is shorter. Species susceptibility to attack varies. In some
species such as hemlock, the host is rarely killed because of its ability to compartmentalize the
decay in the butt log. In other species, notably pines and grand fir, the disease causes tree
death. Trees are often killed standing rather than being windthrown.
Predisposing agents: Certain management practices such as harvesting old growth can create heavy
inoculum levels. If the old stumps become infected subsequent regeneration will alsobecome
infected. This creates a potential for future disease spread that is very serious, as windborne
spores could be carried for some distance. Stumps less than 18" in diameter rarely become
established infections. Partial or selective harvesting increases the likelihood of infection by
creating new stumps and causing basal wounds from mechanical injury. Annosus is itself a
predisposing factor for bark beetle (particularly fir engraver) attack, and is frequently found
on the same tree with Armillaria root rot or laminated root rot.
Impact: Total losses in board feet are not known, but Annosus causes damage by tree killing, butt
rot, windthrow, and decrease in growth of affected trees. Losses due to Annosus are known to be
increasing, probably as a result of intensified logging. Bark beetle epidemics mask the incidence
of root disease by being the obvious killer, but many if not most trees killed by bark beetles
are predisposed by root diseases. Additionally, bark beetle epidemics become established in
diseased trees and spread out to healthy ones.
Management: It is important to search carefully for signs of other root diseases once Annosus has
been diagnosed, as they often occur together. The presence of Armillaria or laminated root rot
will affect choice of species for reforestation and silvicultural methods to follow. Unlike the
other two major root diseases, there is a chemical control for Annosus. Borax powder spread 1/8"
thick on a cut stump within two days of harvest will prevent colonization by Annosus
spores. Stumps smaller than 18" in diameter need not be treated with borax as they rarely become
sources of inoculum. Pine stumps should only be treated if they are within one mile of an
infected pine stand.
--- http://www.forestpests.org/southern/annosusbuttrot.html
Annosus root and butt rot probably enters the stand when fungal spores land on fresh cut stump
surfaces. The fungus grows through the remaining root system into nearby live trees via root
grafts or contacts. Mortality usually begins 2 to 3 years after thinning and often ceases 5 to 7
years later. Damage increases with the sand content of the soil. Twelve inches (30 mm) or more of
sand or sandy loam above a clay subsoil in a soil with good internal drainage is considered a
high hazard site for tree mortality.
--- death circle
The "death circle" in Hartig's (1894) textbook description of annosus root disease nearly a
century ago has become an all too familiar sight in conifer stands throughout the north
temperate region. Even then, he recognized tree-to-tree spread of Trametes radiciperda Hartig
(equals Heterobasidion annosum (Fr.] Bref.) via root contacts, but it was not until more than
50 years later when Rishbeth (1951) made the connection by showing the potential for disease
initiation through plantation thinning and basidiospore colonization of fresh-cut stumps,
thereby reaching adjacent trees.species, much like that of spruce in Europe.
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* email exchange with bob edmonds, assoc dean for research, uw college of forest resources (4 nov 2008)
-- my opening question
-- bob's first respsonse
Hemlock adelgids doesn't seem to be a problem for western hemlock, although it is common on the
foliage in Seattle. On the other hand, many of the hemlocks in Seward Park are suffering from a
fungal root disease (Annosus root and butt rot) that has killed quite a few trees. Many of these dead
trees are still standing. Also it makes them more susceptible to wind throw when we have one of our
periodic wind storms, so many trees have either blown down completely or a leaning on other
trees. These trees usually die as well.
Annosus root and butt rot is a native disease that spreads by airborne spores and enters through
wounds in the stem or roots. It can also spread by mycelium trhough the roots from one tree to
another. Hemlock commonly root grafts so it is easy for the fungus to spread. It doesn't have to go
"outside" into the soil. There isn't a cure for the disease once trees are infected,
unfortunately. Keeping them healthy and not wounded is obviously important. Removal of stumps and
roots is helpful in removing fungal inoculum (it can live for many years in stumps and roots). This
is pretty drastic and is usually not practiced in urban parks.
Unfortuantely, there are other root diseases killing the Douglas-firs in Seward Park (Laminated
root rot and in the older trees the velvet top fungus). Overall many of the trees in Seward Park
aren't all that healthy and there is a worry about hazard trees. On the other hand these are all
native diseases that create gaps in the forest and increase biodiversity and bird and animal habitat
(so that is a plus). It is a great place to take students for pathology and ecology field trips.
-- my follow up
Thanks very much. It's not good news, of course. If you have a further moment to reply, may
I ask a couple of quick additional questions?
1) Are these diseases picking up steam in the urban forests? If so, due to what factors? Pollution?
Other factors?
2) Is there anything a citizen naturalist can do ... other than to watch, learn, and maybe cultivate :} a sense
of detachment about the loss of these beautiful old trees?
-- bob's second reply
Global warming could be having some effect. Certainly the last 10 years has warmed fairly rapidly
and perhaps causing increasing stress to the hemlocks. I don't think air pollution in Seattle is
causing a large problem.
The large old Douglas-fir trees are susceptible to the velvet top fungus even in natural
old-growth forests. For example, in the Hoh Rain forest in Olympic National Park the 650
year-old Douglas-firs are slowly dieing and will never be replaced naturally because you need a
huge fire like the one that established them 650 years ago. That won't happen so the forest is
slowly becoming just a cedar/hemlock forest.
Forests change naturally and trees die. However, loss of the old trees in Seward Park results in
more hardwoods and a forest that doesn't look or feel as attractive to me. I suppose one could
think about ecosystem restoration. They are trying to do this in the Cedar River Watershed to
speed up succession to create old-growth conditions.
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* pests
black-headed budworm
hemlock looper
wooly adelgid
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* western hemlock looper
Lambdina fiscellaria lugubrosa
http://www.forestry.ubc.ca/fetch21/FRST308/lab5/lambdina_fiscellaria_lugubrosa/looper.html
no prolegs except on segments 6 and 10. Broken dark lines on sides and 4 black dots on dorsum of
each segment when mature. Length is 25 to 30 mm.
In August or September larvae drop to ground on "threads" and pupate in bark crevices or under
debris. Moths emerge to lay eggs within 10 to 14 days.
Adults lay eggs on foliage. Eggs hatch the following spring. Early larval instars feed on new
foliage. Later instars feed on older foliage and clip off small twigs. Injured foliage dries out and
imparts the typical reddish colour of infestations.
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* black-headed budworm
http://www.fs.fed.us/r10/spf/fhp/leaflets/Blaheabud.htm
-- Life history
Black-headed budworms overwinter as eggs. The eggs hatch in late Mayor June and young larvae
begin feeding in unopened buds. Larval feeding and growth coincides with the host's bud and
shoot development. Budworm feeding is typically confined to the current year's
needles. Defoliation of older needles is an indication of large budworm populations. In their
last stage of development, larvae build a pupation shelter by webbing. live and cut needles
together. Pupation occurs from mid-July to mid-August. Moths emerge, mate, and female moths
deposit eggs from late August through September.
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