Agricultural Research

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.

ChartThe 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.