Research Bucks Battle Diseases, Build Better Trees
This is a brief overview in two parts of several ongoing
research projects at Washington State University's Research and
Extension Center in Puyallup. These projects are supported by a
variety of funding sources, including the PNWCTA Advanced Research
Fund. In addition to the cooperators listed for each project, WSU's
Gil Dermott and Kathy Riley are also very involved with these
projects.
Control of Swiss Needle Cast
This work is being done in cooperation with Chal Landgren and
Glenn Ahrens at Oregon State University.
Swiss needle cast (SNC) is a common disease on Douglas-fir
Christmas trees in the Pacific Northwest (PNW). Thirty years ago,
research at WSU Puyallup led to the development of effective
monitoring and control measures for this disease, which in 1981
caused pre-harvest losses of $3.4 million in western Washington and
Oregon. Research showed that a single application of a
chlorothalonil-based fungicide like Bravo Weather Stik, costing
about five cents (1981 cost) per tree, provided effective control
of this disease. Periodic grower surveys during the past 25 years
have shown that the disease monitoring and control program that was
put in place 30 years ago has virtually eliminated SNC from
Christmas tree plantations in the PNW and has improved post-harvest
tree performance.
Recently there have been a number of new fungicides that have been
developed and several companies are interested in determining their
effectiveness in controlling SNC. In 2009 a small test was
conducted to compare the efficacy of a new fungicide (USF2015A)
from Bayer against a standard Echo 720 (chlorothalonil) treatment.
This test was conducted on 20-foot to 30-foot tall trees along the
paths in the Forest Demonstration area at the Astoria, Oregon
Department of Forestry District Office. Trees would have generally
been rated as having "severe" Swiss needle cast infection with only
one to two years of needle retention on the branches. The new
growth on these trees ranged from just breaking out of the bud
sheath to a maximum length of two inches at the time of
treatment.
Three branches were randomly selected on each of 20 trees. On each
tree treatments were applied to a single branch on June 1, 2009
using a CP3 backpack sprayer equipped with an 8002 DriftGuard tip
at 20 psi. Emerging shoots were sprayed until wet on the upper and
lower side of the branch. Treatments consisted of USF2015A at 6.8
oz/100 gallons of water, Echo 720 at 5.5 pts/100 gallons of water
and an untreated control.
To evaluate the effectiveness of the treatments in controlling
SNC, branches were harvested on April 13, 2010 and the effects of
the treatments on needle loss, color and SNC development were
assessed in the laboratory at WSU Puyallup. The loss of 2009
needles was rated on a scale of 0 to 10 (0 = none). The color to
the 2009 needles was rated on the following 1 to 6 scale:
1 = dark green, no yellow or
brown discoloration
2 = green, no yellow or brown
discoloration
3 = slight yellow mottling; needles
still have a green background;
there may be brown spots or tips
4 = dull green needles with
moderate chlorosis; may have brown spots or tips
5 = extensive
yellowing/browning
6 = uniformly yellow; may
have some brown spots or tips.
The effect of
the sprays on disease development was determined using a dissecting
microscope to examine the 2009 needles on each of the branches for
fruiting bodies (pseudothecia) of the pathogen (Phaeocryptopus
gaeumannii) that causes SNC. The incidence of needles with
pseudothecia was rated on a scale of 0 to 10, where 0 =
none, 1 = 1-10 percent, 2 = 11-20 percent, etc... 10 = 91-100
percent of the needles have pseudothecia. The severity of infection
was then rated on a scale of one to six by estimating the
percentage of stomates on the needles that had pseudothecia.
Needles with a rating of 1 = < 1 percent of stomates with
pseudothecia, 2 = 1-10 percent, 3 = 11-25 percent, 4 = 26-50
percent, 5 = 51-75 percent, and 6 = 76-100 percent. An overall
disease rating was obtained by multiplying the incidence rating
(0-10) and severity ratings (1-6). Thus, the overall disease rating
potentially could range from 0 to 60. This rating was then used for
the statistical analysis to determine if the treatments had any
effect on disease development.
Results: The data from this trial indicated that treatments had no
effect on needle loss or color (Table 1). Overall, disease pressure
was fairly low during this test. Applications of Echo significantly
reduced disease development compared to the check or USF2015A,
which were not significantly different from each other (Table 1).
Based on the results of this test, it appears that USF2015A has
limited potential to control SNC on Douglas-fir trees.
In 2010 an additional SNC control trial was established at the
Astoria site. This trial is being partially supported by the USDA
IR-4 program. The trial includes 12 treatments that were applied
during spring 2010 (Table 2). Data is currently being collected to
determine the effect of these treatments on disease development.
Following bud break this spring, these treatments will be reapplied
to the trees in an effort to confirm the results from the 2010-11
trial.
Variation in the Development of CSNN on Various Species
In Cooperation with Chal Landgren, OSU
Current season needle necrosis (CSNN) is a poorly understood
disease that affects a number of true firs (Abies spp.) that are
grown as Christmas trees. CSNN has been reported on noble, Nordmann
and grand fir in Europe and these species, plus Turkish fir, in the
Pacific Northwest. In 2002 and 2004 a series of replicated genetic
field trials were established at grower sites in Washington and
Oregon, as well as the WSU Research Center in Puyallup. The WSU
Puyallup site is a low elevation site that is very conducive to the
development of CSNN. These trials contain a total of 91 sources of
noble fir, 15 sources of Nordmann fir and four sources of Turkish
fir. To examine yearly variation in the development of CSNN,
symptom severity on all the trees at the WSU Puyallup site have
been rated on a scale of 0 to 10, with 0 = none and 10 = >90
percent needles affected, during late summer/early fall.
The overall disease ratings revealed that there has been
significant yearly variation in the average CSNN ratings for the
trees in these trials. Over six years the average overall rating
for the 37 sources of noble fir in the 2002 planting ranged from a
low of 1.5 in 2009 to a high of 3.4 in 2006. Over five years the
average overall rating for the 54 sources of noble fir in the 2004
trial ranged from a low of about 1.1 in 2005 to a high of 3.3 in
2008.
In addition to yearly differences in CSNN development, there have
been significant differences in the susceptibility of the different
sources of trees in these plots. In the 2002 noble fir plot the
percentage of trees that were resistant to CSNN ranged from five
percent to 80 percent, depending on the source. In the 2004 noble
fir plot the range was four percent to 65 percent. Compared to
noble fir, limited CSNN has developed on the Nordmann and Turkish
fir trees. Over four years the yearly average overall ratings for
all the sources of Nordmann and Turkish fir ranged from 0.3 to 0.9
and seven sources had more than 80 percent of the trees that never
developed any CSNN.
Although there was significant yearly variation in the severity of
CSNN, an analysis indicated that there was a highly significant
correlation between the yearly susceptibility rankings of the
noble, Nordmann and Turkish fir sources in each of these plots.
This means that even though there was significant yearly variation
in the overall CSNN rating, the relative susceptibility ranking of
the sources were the same each year.
What happens when we compare the susceptibility rankings of the
sources at Puyallup to their rankings at another site? In 2009 we
compared the severity of CSNN development on trees in the 2004
noble fir genetic test plot at Puyallup to the same sources at
Silver Mountain Christmas Trees near Sublimity, Oregon. The overall
plot CSNN rating for the trees at Silver Mountain was much lower
than Puyallup. Over 94 percent of the trees at Silver Mountain had
no CSNN, compared to only 23 percent at Puyallup. Even though much
less CSNN developed at Silver Mountain, rank order analysis
indicated that there was a highly significant correlation in
susceptibility rankings of the sources at both sites.
Regression analysis of CSNN ratings from Nordmann and Turkish fir
planted in a "valley" and "hill" at Puyallup also indicated that
there was a highly significant correlation between the four-year
average ratings of the individual sources at the valley and hill
sites. These results indicate that there is considerable variation
in the susceptibility of different sources of noble, Nordmann and
Turkish fir to CSNN and that the relative susceptibility of
different sources of trees to CSNN can be determined after one or
two years at conducive sites such as Puyallup.
Recent research in Norway has found that the fungus Sydowia
polyspora is associated with CSNN. Although the exact role of this
fungus in the development of CSNN is still being investigated, we
are working with several cooperators in Norway on a
Norwegian-funded project to determine if there are specific weather
patterns that are associated with the development of CSNN. Disease
development and weather data from the PNW is being provided to
these cooperators who will use this data to determine if there are
certain weather patterns that correlated to disease
development.