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Swiss Needle Cast: Is it coming to
Swiss needle cast?
First described in 1925 in Switzerland,
Swiss needle cast is a disease caused by a fungus which
attacks Douglas-fir forests. It has been tracked in Oregon
since 1981 and has since become increasingly severe, especially
during recent years of abnormally heavy rainfall.
Swiss needle cast occurs through out
the Douglas-fir region of the Pacific Northwest. It is a
particular problem in heavy fog and rainfall regions along
the north Oregon coast where Douglas-fir was planted exclusively
to replace natural forests of mixed tree species following
harvest or fires. It occurs less frequently in inland and
some coastal forests where even-aged stands of predominantly
Douglas-fir had historically evolved from intense stand-replacement
fires. Aerial surveys have mapped nearly 400,000 acresfrom
south of Coos Bay north into western Washingtonthat
display obvious symptoms.
Trees infected by Swiss needle cast
are weakened by a seriously impaired nutrient flow. It's
easiest to spot in late winter through early spring, and
the needles appear noticeably yellow to brownish yellow.
Although the disease rarely kills trees outright, infected
trees often lose all but the current year's growth of needles.
This allows more light to enter the forest floor, promoting
the growth of competing understory vegetation that reduces
nutrients available to diseased trees and further inhibits
One study of an infected stand showed
a reduction of more than 20 percent in volume growth. While
it hasn't happened yet, scientists fear that trees weakened
by the disease will be attacked and killed by opportunistic
a Douglas-fir infected by Swiss needle cast
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causes Swiss needle cast?
Scientists suspect that a key cause
for its flare up is certain forest management practices
made worse in recent years by abnormally wet climate favorable
to the fungus.
Historically, much of the coastal forest
was a mix of hemlock, cedar, hardwoods, and Douglas-fir.
Because Douglas-fir is the most desired commercial species,
it has been the choice for replanting harvested areas for
the last half century. Some scientists believe this change
from tree species diversity to a forest consisting primarily
of Douglas-fir has upset the balance between the forest
and the fungus, with the wet climate setting the stage for
an upsurge in the disease to a point where it has overwhelmed
the forests' natural defenses.
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effect will Swiss needle cast have at the mill?
Research is being conducted on the effect
of the disease on wood structure. Badly infested trees may
have more "late" (summer) wood and less "early"
(spring) wood. It's not yet clear what affect that will
have on the quality of lumber and other products made from
diseased wood, but an ongoing epidemic of the disease would
affect the quantity of timber available for forest products..
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we do about it?
Research suggests that Douglas-fir grown
from non-local seed sources may be more vulnerable to needle
caste. Foresters can help avoid the disease by using seedlings
grown from local parent trees that have built up a resistance.
There has been reluctance by some forest landowners to replant
with less valuable species of the past, but many foresters
now are addressing the problem by replanting a mix of species
rather than just Douglas-fir in harvested areas and by planting
hemlock, which is not susceptible to the disease, in their
worst-hit stands.. Selective thinning that favors hemlock
and other non-host species is another promising management
technique. These measures will move us toward a diverse
species composition that will provide some insurance against
increasing damage from the disease.
Fungicides and fertilization of affected
stands have shown little promise, but research continues
on minerals and other soil additives. In severely affected
stands, stand replacement may be the best option.
We have much to learn about the disease,
and its magnitude will not be known until we have completed
more research and monitoring. The Swiss Needle Caste Cooperative,
in cooperation with the Oregon Department of Forestry's
Insect and Disease Unit, has installed permanent growth
monitoring plots on private and public forestlands, and
damage from the disease is being tracked through a combination
of aerial and ground survey. Data from these studies will
help scientists estimate the disease's severity and range
as well as changes in stand conditions over time.
We have learned that planting single-species
forests in heavy fog and rainfall regions where mixed species
of trees historically grew has unintended consequences on
forest health. Foresters will continue to learn from experience
and research as well as from nature as they seek the best
way to manage forests.
- Dr. Greg Filip, OSU College of Forestry
- Dave Odgers, OFRI
- Forest Health Note, Oregon Dept.
of Forestry, March 1998.
For more information, visit the
Needle Cast Cooperative Web
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