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Fungal disease of true firs attacking
Christmas trees
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John Schmitz, June 28, 2002, The Capital Press
SALEM - The Northwest Christmas tree industry is becoming
increasingly alarmed over the spread of a relatively new
disease to them called annesus root rot, which attacks
only true firs.
The disease, which is spread by airborne fungal spores
that waft into recently harvested plantations and land
on stumps, is showing up in more and more true fir, multiple-rotation
farms where stumps arent removed after harvest. Once established,
annosus spreads when roots of infected harvested trees
come in contact with the roots of new seedlings. "Clearly,
in some fields growers are losing thousands and thousands
of dollars per acre," said Washington State University
plant pathologist Gary Chastagner, who has been studying
the disease."A lot of the growers are running into
proble* ms when planting true firs, particularly when
they follow a true fir crop."
| "A lot of growers are
running into problems when planting true firs,
particularly when they follow a tree fir crop".
Gary Chastagner, Washington State University
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Chastagner, who works out of WSU's
Puyallup Research and Extension Center, presented a talk
on annosus root rot at the recent summer meeting of the
Pacific Northwest Christmas Tree Association in
Portland. "We're seeing a fair amount of mortality
in some plantations," he said after his talk. "We've
got about 19 or so plantations that we've been mapping,
starting last year. The percentage of trees infected ranges
from relatively small to a maximum of about 30%".
In fact, Chastagner found the fungus in two of the plantations
that were on this year's PNWCTA farm tour.
Disease spread
The disease is having an especially heavy impact on Northwest
Christmas tree production because it is partial to true
firs, such as Nobles, which have been skyrocketing in
popularity in recent years because of their superior needle
retention.
Above ground, reddish-brown trees infected with annosus
can resemble those infected with either phytophthora or
armillaira, Chastagner said. The discoloring starts prior
to or shortly after bud
break. "In some cases there can be branch flagging."
Across section of a tree cut at the base will tell whether
or not the tree is indeed infected with annosus. The telltale
sign is gray
to brown discoloration that runs across growth rings.
Annosus is a secret invader in that marketable trees can
be infected with the disease and show no above-ground
symptoms. Which is why Chastagner encourages growers to
inspect freshly cut stumps and also the butts of trees
as they are stacked in plantations during harvest. Growers
who follow true fir harvests with true fir plantings and
don't remove the stumps are asking for trouble.
"Historically, growers will plant next to stumps
or between stumps without doing any site renovation in
between rotations."
Annosus has established a bad reputation in certain forested
sites, particularly pine, Chastagner said. It's only been
in the last several years that it's been creeping into
Christmas tree plantations. The disease was first discovered
in Northwest Christmas trees in an Oregon plantation in
1983. "But now it's much more prevalent. In the past
it has been evident on trees near the end of the rotation,
but now we're seeing
trees being killed within a few years of planting as well
as later in the rotation."
Control
Once annosus strikes a plantation, the only safe measure
is to remove infected stumps and roots.
Any fungal material left behind will be naturally dealt
with by beneficial soil microbes, which out-compete annosus.
As long as an infected stump and its roots stay intact
in the ground, how ever, the fungus will live on. There
are several treatments that can be used to prevent annosus
spores from colonizing fivshly cut stumps, all of which
should be applied as soon after harvest as possible. One
is with a dry granular fungicide called Sporax (Wilbur-Ellis),
which is simply sprinkled on the cut surfaces of stumps.
A
20 percent spray of a urea/water mixture applied to stumps
has also proved effective in lab tests.
Since beneficial microbes in soils have been shown to
out compete and eliminate the annosus fungus, simply kicking
or shoveling some dirt onto the stump at harvest time
is a low-cost alternative.
Chastagner said that most of the research on the effectiveness
of the various annosus treatments has been conducted in
forest settings only. For that reason, he's conducting
several fungicide trials in
Christmas tree plantations. He hopes to have the results
in time for the PNWCTA trade fair in Portland, Ore., in
September.
Chastagner said that the annosus-infected roots of just
one tree can potentially spread the disease to up to 10
seedlings plant ed near it. "It doesn't take many
trees to be killed to add up to a
significant amount of money." It's highly unlikely
that annosus is spread by infected nursery stock, Chastagner
said. "The most likely source is diseased timber
stands in the vicinity of plantations." Spores can
spread for miles.
Testing labs
Growers who suspect annosus should collect root and bark
samples and send them either to the plant clinic lab in
Puyallup or Oregon State University. They should call
first for instructions
on sample collection and shipping. For WSU, call (253)
445-4501;for OSU, call (541) 737-3472.
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