Needle Cast Disease Research Articles

Effects of needle cast diseases on the growth of a 33-year-old Douglas-fir provenance plantation in northwestern Bulgaria

Abstract In this study, the effects of defoliation caused by fungal pathogens on the tree vitality and growth of a 33-year old Douglas-fir (Pseudotsuga menziesii) provenance plantation in northwestern Bulgaria was presented. The results of the conducted surveys in 2011 and 2020 showed that there were significant differences between the individual provenances of Douglas-fir concerning their susceptibility to the needle cast diseases, caused by the fungal pathogens Rhabdocline pseudotsugae and Phaeucryptopus gaeumannii. The extent of damage, expressed as the amount of Douglas-fir needles cast, varied among provenance groups in individual years. A serious degree of defoliation was assessed among all continental provenances. In 2011, all examined trees from the group of continental provenances had severe symptoms of the needle cast disease. In 71.5% of them, the defoliation of the crowns was over 25% – moderately to severely affected. The average degree of defoliation varied from 18.3% (32 Wаrm Springs) to 89.3% (55 Alamogordo). In 2020, severe defoliation was found among all continental provenances. Both fungal pathogens were found as causes of the defoliation of 64.3% of the trees. The growth indicators: average height, average diameter at breast height, average height- and diameter increment for survived provenances in 2011 (at age 24) and 2020 (at age 33) were evaluated. The loss of needles and the reduced physiological function of the trees affected their vitality in the following years. Relationships between the average current annual height and diameter increment by provenance groups for 2003–2011 and 2011–2020 were calculated. It was found that with an increase in the degree of defoliation, the height and diameter increment of the provenances decreases.

First report of Cryptocline taxicola (Helotiales: Helotiaceae) causing needle cast disease on common yew in Algeria

AbstractThis short report describes the occurrence of Cryptocline taxicola (Allesch.) Petr. causing needle cast on Taxus baccata L. trees in natural stands in Algeria. Symptoms of fungal infection were observed on the trees' crowns. Closer inspection of collected needles showed the presence of dark brown fungal fruiting bodies on the upper and the lower sides of the needles. The visual symptoms and the microscopical study allowed the fungus to be identified as C. taxicola. This is the first report of this pathogen in Algeria. A detailed description of the fungus is given.

Genetic Lineage Distribution Modeling to Predict Epidemics of a Conifer Disease

A growing body of evidence suggests that climate change is altering the epidemiology of many forest diseases. Nothophaeocryptopus gaeumannii (Rhode) Petrak, an ascomycete native to the Pacific Northwest and the causal agent of the Swiss needle cast (SNC) disease of Douglas-fir [Pseudotsuga menziesii (Mirbel) Franco], is no exception. In the past few decades, changing climatic conditions have coincided with periodic epidemics of SNC in coastal forests and plantations from Southwestern British Columbia (B.C.) to Southwestern Oregon, wherein an increase in the colonization of needles by N. gaeumanii causes carbon starvation, premature needle shedding and a decline in growth. Two major sympatric genetic lineages of N. gaeumannii have been identified in the coastal Pacific Northwest. Past research on these lineages suggests they have different environmental tolerance ranges and may be responsible for some variability in disease severity. In this study, we examined the complex dynamics between biologically pertinent short- and long-term climatic and environmental factors, phylogenetic lineages of N. gaeumannii and the severity patterns of the SNC disease. Firstly, using an ensemble species distribution modeling approach using genetic lineage presences as model inputs, we predicted the probability of occurrence of each lineage throughout the native range of Douglas-fir in the present as well as in 2050 under the “business as usual” (RCP8.5) emissions scenario. Subsequently, we combined these model outputs with short-term climatic and topographic variables and colonization index measurements from monitoring networks across the SNC epidemic area to infer the impacts of climate change on the SNC epidemic. Our results suggest that the current environmental tolerance range of lineage 1 exceeds that of lineage 2, and we expect lineage 1 to expand inland in Washington and Oregon, while we expect lineage 2 will remain relatively constrained to its current range with some slight increases in suitability, particularly in coastal Washington and Oregon. We also found that disease colonization index is associated with the climatic suitability of lineage 1, and that the suitability of the different lineages could impact the vertical patterns of colonization within the crown. We conclude that unabated climate change could cause the SNC epidemic to intensify.

Molecular Identification and Antifungal Activity of a Defensin (PaDef) from Spruce

Defensins, as part of the PR protein family, not only have antimicrobial activity in vitro, but also play an important role in plant disease resistance. To explore the molecular function of defensin in spruce, a defensin gene PaDef was isolated and characterized from Picea asperata. The full-length cDNA sequence of the PaDef was 264 bp and contained an ORF of 252 bp, encoding a total of 83 amino acids. The deduced PaDef protein belongs to the gamma-thionin family and contains the Knot1 domain and eight conserved cysteine residues. Blast and phylogenetic analysis showed that the PaDef protein shared high homology with other plant defensin proteins. The tertiary structure of PaDef was obtained by homologous modelling using the structure of Pinus sylvestris defensin as a template and exhibited a βαββ structure. SDS-PAGE analysis showed that the molecular mass of recombinant PaDef expressed in Escherichia coli was 23.8 kDa. Plate assay showed that purified PaDef exhibited strong antifungal activity inhibiting the growth of Pestalotiopsis neolitseae, but not Colletotrichum gloeosporioides and Botrytis cinerea. Microscopic observation revealed that purified PaDef had a negative effect on the hyphal morphology of all three phytopathogens. qRT-PCR analysis indicated that the PaDef gene had the highest expression level in needles of P. asperata compared with roots, phloem, twigs, and could be significantly upregulated by the pathogenic fungus Lophodermium piceae, which causes needle cast disease. These results provide a molecular basis for determining the molecular function of defensin PaDef in P. asperata and its potential as an antifungal agent.

Analysis of Swiss needle cast disease on Pseudotsuga menziesii var. glauca within a Christmas tree plantation in Mexico

AbstractNothophaeocryptopus gaeumannii causes Swiss needle cast disease in Douglas‐fir forest trees and ornamental plantations. This study analysed disease and pathogen behaviour from summer 2011 to spring 2012. An untreated plot within a Pseudotsuga menziesii var. glauca plantation in Valle de Bravo, Mexico was divided into 12 sub‐plots. At each sampling date, needles were collected from four trees per sub‐plot. The analysis included seven needle age cohorts from branches from two canopy sections, as well as fallen needles from five random trees inside the entire plot. Airborne ascospores were collected weekly in slide traps. Sequencing identified the pathogen from DNA extracted from 18 mycelial colonies (isolates) and ascospores DNA from four selective slide traps. Disease and pathogen characteristics were mostly similar to other reports, except for ascospores inside pseudothecia on the youngest age class of foliage. Defoliation affected lower canopies frequently, while in the middle canopy it ranged from 6% to 98% depending on the needle age. In fallen needles, mature pseudothecia contained ascospores and isolated colonies developed in an agar‐based medium. Ascospore fluctuation peaked in two periods, but the most relevant occurred from 11 February to 17 March 2012, coinciding with bud break. These results contribute further understanding of SNC disease useful in improving the health of Christmas trees and the less‐studied P. menziesii var. glauca.

Contrasting the Pathogen Loads in Co-Existing Populations of Phytophthora pluvialis and Nothophaeocryptopus gaeumannii in Douglas Fir Plantations in New Zealand and the Pacific Northwest United States.

The emergence of Phytophthora pluvialis as a foliar pathogen of Douglas fir in New Zealand and the Pacific Northwest United States has raised questions about its interaction with the widespread Swiss needle cast (SNC) disease. During Spring 2017, we repeatedly sampled 30 trees along an environmental gradient in each region and 292 additional trees in a longitudinal transect to assess the P. pluvialis epidemic and the association between P. pluvialis and Nothophaeocryptopus gaeumannii, which are causal agents of SNC. Both pathogens were consistently more abundant in the host's exotic environment in New Zealand. In both areas, the two pathogens co-exist in different spatial scales for regions and needles. The relative abundance of both pathogens was negatively correlated in the Pacific Northwest, where both presumably have co-existed for longer. Our findings confirmed the interaction of P. pluvialis and N. gaeumannii as foliar pathogens of Douglas fir and suggest a within-site spatial variation in the Pacific Northwest.

Cloning, Characterization and Expression of the Phenylalanine Ammonia-Lyase Gene (PaPAL) from Spruce Picea asperata

Phenylalanine ammonia-lyase (PAL) is the crucial enzyme of the phenylpropanoid pathway, which plays an important role in plant disease resistance. To understand the function of PAL in Picea asperata, in this study, the full-length cDNA sequence of the PAL gene from this species was isolated and named PaPAL. The gene contains a 2160-bp open reading frame (ORF) encoding 720 amino acids with a calculated molecular weight of 78.7 kDa and a theoretical isoelectric point of 5.88. The deduced PaPAL protein possesses the specific signature motif (GTITASGDLVPLSYIA) of phenylalanine ammonia-lyases. Multiple alignment analysis revealed that PaPAL has high identity with other plant PALs. The tertiary structure of PaPAL was predicted using PcPAL from Petroselinum crispum as a template, and the results suggested that PaPAL may have a similar function to that of PcPAL. Furthermore, phylogenetic analysis indicated that PaPAL has a close relationship with other PALs from the Pinaceae species. The optimal expression condition of recombinant PaPAL in Escherichia coli BL21 (DE3) was 0.2 mM IPTG (isopropyl β-D-thiogalactoside) at 16 °C for 4 h, and the molecular weight of recombinant PaPAL was found to be approximately 82 kDa. Recombinant PaPAL was purified and exhibited high PAL activity at optimal conditions of pH 8.6 and 60 °C. Quantitative real-time PCR (qRT-PCR) showed the PaPAL gene to be expressed in all tissues of P. asperata tested, with the highest expression level in the needles. The PaPAL gene was induced by the pathogen (Lophodermium piceae), which caused needle cast disease, indicating that it might be involved in defense against needle cast disease. These results provide a basis for understanding the molecular mechanisms of the PAL gene in the process of P. asperata disease resistance.

A dynamical systems model for poly-cyclic foliar forest pathogens

A simple systems model is proposed to understand and quantify the onset and epidemiology of red needle cast in radiata pine. This disease is impacting much of the New Zealand forestry estate being driven through the production of self-replicating spores which are dispersed with water. The model is at present deterministic, not spatially or age-structured, nor dependent on environmental or seasonal effects. This model shows the clear existence of calculable thresholds for disease proliferation and elimination, showing it has captured the essential components of the biological mechanisms. It is to be used to identify thresholds for infection to spread or retract. Further it will provide a base model from which we can fit and then predict experimental outcomes. References C Lee Campbell, Laurence V Madden, et al. Introduction to plant disease epidemiology. John Wiley and Sons., 1990. Margaret Anne Dick, Nari Michelle Williams, Martin Karl-Friedrich Bader, Judy Frances Gardner, and Lindsay Stuart Bulman. Pathogenicity of phytophthora pluvialis to pinus radiata and its relation with red needle cast disease in new zealand. New Zealand Journal of Forestry Science, 44(1):6, 2014. Heidi S Dungey, Nari M Williams, Charlie B Low, and Graham T Stovold. First evidence of genetic-based tolerance to red needle cast caused by phytophthora pluvialis in radiata pine. New Zealand Journal of Forestry Science, 44(1):31, 2014. RJ Ganley, NM Williams, CA Rolando, IA Hood, HS Dungey, PN Beets, LS Bulman, et al. Management of red needle cast, caused by phytophthora pluvialis, a new disease of radiata pine in new zealand. N. Z. Plant Protect.-SE, 67:48–53, 2014. Wake GC. Private communication, 2017. Christopher A Gilligan. An epidemiological framework for disease management. Advances in botanical research, 38:1–64, 2002. MJ Jeger. Asymptotic behaviour and threshold criteria in model plant disease epidemics. Plant Pathology, 35(3):355–361, 1986. Nurul S Abdul Latif, Graeme C Wake, Tony Reglinski, and Philip AG Elmer. Modelling induced resistance to plant diseases. Journal of theoretical biology, 347:144–150, 2014. Nurul S Abdul Latif, Graeme C Wake, Tony Reglinski, Philip AG Elmer, and Joseph T Taylor. Modeling induced resistance to plant disease using a dynamical systems approach. Frontiers in plant science, 4, 2013. Laurence V Madden, Gareth Hughes, Frank Bosch, et al. The study of plant disease epidemics. American Phytopathological Society (APS Press), 2007. CA Rolando, MA Dick, J Gardner, M Bader, NM Williams, et al. Chemical control of two phytophthora species infecting the canopy of monterey pine (pinus radiata). Forest Pathology, 47(3), 2017. Carol Rolando, Robyn Gaskin, David Horgan, Nari Williams, and Martin KF Bader. The use of adjuvants to improve uptake of phosphorous acid applied to pinus radiata needles for control of foliar phytophthora diseases. New Zealand Journal of Forestry Science, 44(1):8, 2014.

A likelihood-based time series modeling approach for application in dendrochronology to examine the growth-climate relations and forest disturbance history

A time series intervention analysis (TSIA) of dendrochronological data to infer the tree growth-climate-disturbance relations and forest disturbance history is described. Maximum likelihood is used to estimate the parameters of a structural time series model with components for climate and forest disturbances (i.e., pests, diseases, fire). The statistical method is illustrated with a tree-ring width time series for a mature closed-canopy Douglas-fir stand on the west slopes of the Cascade Mountains of Oregon, USA that is impacted by Swiss needle cast disease caused by the foliar fungus, Phaecryptopus gaeumannii (Rhode) Petrak. The likelihood-based TSIA method is proposed for the field of dendrochronology to understand the interaction of temperature, water, and forest disturbances that are important in forest ecology and climate change studies.

Assessment of climatic limits of needle cast–affected area under climate change in Central Siberia

The relationships between climate (January and July temperatures, annual precipitation, and a relative moisture index) and the number of foci and intensity of the needle cast disease caused by fungi from the genus Lophodermium Chevall. in the Scots pine nurseries and provenance trials in Krasnoyarsk krai have been studied using multivariate statistics methods. It is found that peaks in the disease occurrence are related to the warm and humid weather conditions. Bioclimatic models of the needle cast ranges have been built using the climate variables; the spatial dynamics of the disease occurrence have been projected under various scenarios of climate warming over the 21st century. Model experiments have shown that the needle cast disease would shift northwards into the new regions in Krasnoyarsk krai, where the phytopathogen has not yet been registered in the nurseries. The largest forest areas exposed to needle cast disease are predicted to be at a high risk of outbreaks by 2020 under moderate climate warming. With a significant warming trend by 2080, potential risk areas will be reduced, because the pine expansion into the permafrost zone should be limited by slow thawing of its active layer.

Douglas-fir displays a range of growth responses to temperature, water, and Swiss needle cast in western Oregon, USA

Abstract Douglas-fir ( Pseudotsuga menziesii var. menziesii (Mirb.) Franco) growth in the Pacific Northwest is affected by climatic, edaphic factors and Swiss needle cast (SNC) disease. We examine Douglas-fir growth responses to temperature, dewpoint deficit (DPD), soil moisture, and SNC using time series intervention analysis of intra-annual tree-ring width data collected at nine forest stands in western Oregon, USA. Air temperature, previous-year DPD and SNC and their interactions were the primary factors influencing tree growth at all sites, whereas other key seasonal climatic factors limiting growth varied by site. Winter temperature was more important at high elevation cool sites, whereas summer temperature was more important at warm and dry sites. Growth rate increased with summer temperature to an optimum ( T opt ) then decreased at higher temperatures. At drier sites, temperature and water affected growth interactively such that T opt decreased with decreasing summer soil moisture. With increasing temperature due to climate change, growth rates increased at high elevation sites and declined at mid-elevation inland sites since ∼1990. Growth response to climate and SNC are confounded at all sites. We conclude that as temperature rises and precipitation patterns shift toward wetter winters and drier summers, Douglas-fir will experience greater temperature and water stress and an increase in severity of SNC.

Pathogenicity of Phytophthora pluvialis to Pinus radiata and its relation with red needle cast disease in New Zealand

Background Red needle cast, a new foliage disease of Pinus radiata in New Zealand is described. The disease has been variable in incidence and severity both regionally and in different years. The early symptoms of discrete olive coloured lesions, often with a narrow dark resinous mark or band, were first recognised in winter of 2008 in plantation forests on the eastern coast of the North Island. These lesions develop further to result in rapid needle senescence and premature defoliation. The disease has been termed red needle cast in New Zealand as affected trees have a reddish appearance prior to the casting of the needles. The subsequent four years of monitoring have confirmed that, depending on location, symptoms are first observed in late autumn through late winter. Newly developing spring and summer foliage is seldom affected. Isolation from needles using a Phytophthora-selective medium frequently yielded an unknown species of Phytophthora which was subsequently found to be identical to Phytophthora pluvialis, a species described from Oregon, USA in 2013 where it is not associated with disease. Infection appears to be limited to the needles with no recoveries of Phytophthora pluvialis having been made from the roots, stems or branches. Occasionally a second species of Phytophthora, P. kernoviae, was also recovered from needles with the same symptoms.

Thinning Mixed-Species Stands of Douglas-Fir and Western Hemlock in the Presence of Swiss Needle Cast: Guidelines Based on Relative Basal Area Growth of Individual Trees

In coastal forests of the Pacific Northwest, young coniferous plantations typically contain a mixture of planted and natural Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla). Swiss needle cast (SNC) disease inhibits the growth of Douglas-fir to varying degrees in these stands, depending on SNC severity. In addition to the value differential between Douglas-fir and western hemlock, foresters must account for differences in growth potential (tree size, competitive position, site characteristics, disease pressure) when selecting trees for retention during thinning operations. Diameter increment models for Douglas-fir and western hemlock were developed from permanent plot data collected for the SNC growth impact study (GIS), precommercial thinning study (PCT), commercial thinning study (CT), and retrospective commercial thinning study (RCT). Predictor variables represent tree size, competitive position, site characteristics, and SNC severity. SNC severity was indexed by foliage retention, defined as the number of annual needle cohorts held by a tree. Foliage retention was positively correlated with Douglas-fir diameter increment and negatively correlated with western hemlock diameter increment. Charts developed from the diameter growth models provide a field tool for assessing the relative basal area growth of adjacent Douglas-fir and western hemlock of a given initial diameter in a stand of given SNC severity. In a stand with severe SNC (foliage retention 1.5 years) the basal area growth of a 6-in. western hemlock tree will exceed the basal area growth of any Douglas-fir tree up to 7.7 in. in DBH. In a relatively healthy stand (foliage retention 3.0 years) the basal area growth of 6 in. Douglas-fir and western hemlock trees will be approximately equivalent.

Fertilization impacts on Swiss needle cast disease severity in western Oregon

The influence of fertilization on disease severity is unknown in most forest pathosystems. Fertilization treatments were randomly applied to 0.01ha plots centered on individual dominant or co-dominant Douglas-fir trees in ten Douglas-fir stands from coastal Oregon to the foothills of the Oregon Cascade Range, USA. This region is affected by Swiss needle cast, caused by the fungal pathogen Phaeocryptopus gaeumannii. Selected stands represented a range of Swiss needle cast disease severity, and 10 replications of each fertilization treatment were applied in each stand. The six treatments included nitrogen (urea), calcium as lime (calcium carbonate), calcium as calcium chloride, phosphorus (monosodium phosphate), a site-specific blend (Kinsey) and an unfertilized control. Fertilization took place from February–April 2007, and single branches were collected from treated trees for disease severity assessment of foliage in May 2010. Disease severity of 1- and 2-year-old needles was evaluated by counting the frequency of infected needles and the density of P. gaeumannii fruiting bodies (pseudothecia) on a random subset of needles from each tree and needle age class. Fertilization treatment effects on infection index (mean fruiting body density) were tested by mixed-effects models that accounted for site as a blocking factor. Treatment effects on infection index at each of the study locations were also tested by ten separate ANOVAs. Across and within sites, fertilization treatment did not significantly affect infection index of 1- or 2-year old needles (p>0.05). Small differences in mean fruiting body density (⩽3%) between fertilization and control treatments across sites were not statistically significant, nor are they believed to be biologically or economically significant. Decisions regarding fertilization should be based on site-specific attributes, such as soil chemistry. There is no evidence that fertilization directly ameliorates or exacerbates Swiss needle cast severity in western Oregon.

Lophodermium needle cast, insect defoliation and growth responses of young Scots pines in Estonia

SummaryUsing a retrospective approach, based on historical needle cast disease and insect pest records, data series of needle losses (reconstructed by the use of the needle trace method), tree growth parameters and meteorological data were studied to determine the impact of the appropriate pointer (epidemic or calamity) years on the annual radial and height increment of 46 sample trees in six Scots pine (Pinus sylvestris) stands in Estonia from 1887 to 2006. First, the needle cast epidemics during the last 120 years were retrospectively determined, with resulting 4.6 epidemics per decade as a mean frequency. If the sum of precipitation from May to August reached 300 mm (the mean of 12 epidemic years studied: 361 ± 15 mm), an epidemic of needle cast caused byLophodermium seditiosummight follow the next year in young plantations. For insect defoliators, similarly clear triggering threshold values of precipitation or temperature could not be determined, although dry and warm summers and mild winters supported the calamities. We separately detected that both larger needle losses and growth reductions in trees related to Lophodermium needle cast epidemic years lasted until the same age of pines, 22–24 years, but for insect pest (diprinoid sawflies) calamity years the growth reduction lasted longer. The relevance of these findings for the prediction of Lophodermium needle cast epidemics is briefly discussed.

Fungus Slows Fir

![Figure][1] Sick old Douglas firs look like bottle brushes. CREDIT: DAVE SHAW/OREGON STATE UNIVERSITY A tree fungus that used to be a minor nuisance is now causing a major loss of growth in Douglas firs, a staple of the timber industry in the Pacific Northwest. Swiss needle cast disease

Taper and Volume Responses of Douglas-Fir to Sulfur Treatments for Control of Swiss Needle Cast in the Coast Range of Oregon

Abstract For nearly 20 years, foresters in the Oregon Coast Range have been witnessing a substantial decease in Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco.) vigor and volume, caused by Swiss needle cast (SNC) disease. Currently, there are no solutions and disease severity is expected to worsen in coming years, but there is hope that aerially applied treatments of sulfur may be able to alleviate the effects of SNC. In this trial, volume, taper, and other attributes were examined on 120 Douglas-fir trees heavily infected with SNC for response to treatments of (1) sulfur, (2) sulfur + nutrients, and (3) control, which received no treatment. Tree attributes such as crown ratio, crown width, and sapwood area at crown base showed no statistically significant differences between treatments. Means of both foliage mass and years of needle retention also were not different between sulfur and control treatments. However, both of these attributes were different between the sulfur + nutrient and control treatments (P = 0.0599, 0.0205). Using a modified Kozak's (1988) variable exponent model form, taper analysis indicated that the taper of trees within the sulfur treatment was not significantly different from the taper of the control, while the sulfur + nutrient treatment showed decreased taper compared with the control (P =<0.0246). This improvement of taper in the sulfur + nutrient stand, however, has not translated into a statistically significant increase in cubic foot volume removed in the first thinning after adjusting for tree size differences between treatments. Comparing treatments by monetary value of removed trees in the first thinning also showed no significant differences, thereby implying that sulfur and sulfur + nutrient treatments are not able to increase volume enough in 4 years to produce additional profits in the first commercial thinning. It should be noted, however, that all conclusions drawn from this study are essentially from a single replication, and the scope of inference applies only to this particular type of stand in the Oregon Coast Range.

Predicting effects of climate change on Swiss needle cast disease severity in Pacific Northwest forests

Swiss needle cast of Douglas-fir (Pseudotsuga menziesii) is caused by the ascomycete Phaeocryptopus gaeumannii. Symptoms are foliage chlorosis and premature needle abscission due to occlusion of stomata by the ascocarps of the pathogen, resulting in impaired needle gas exchange. Growth losses of 20%-50% due to Swiss needle cast have been reported for approximately 150 000 ha of Douglas-fir plantations in western Oregon since 1996. In the western Coast Range of Oregon and in New Zealand, winter temperature is strongly correlated with pathogen abundance. Models for predicting disease severity based on winter temperature account for 77% and 78% of the variation in 1- and 2-year-old needles, respectively, for western Oregon sites and approximately 80% for New Zealand. A trend of temperatures increasing by 0.2–0.4 °C during the winter months and spring precipitation increasing by 0.7–1.5 cm/decade since 1970 suggests that regional climate trends are influencing the current distribution and severity of Swiss needle cast disease. Continuing winter temperature increases predicted for the Pacific Northwest of approximately 0.4 °C/decade through 2050 suggest that the severity and distribution of Swiss needle cast is likely to increase in the coming decades as a result of climate change, with significant consequences for Pacific Northwest forests.

Distribution of Swiss needle cast in New Zealand in relation to winter temperature

Phaeocryptopus gaeumannii, the causal agent of Swiss needle cast disease, is widely distributed throughout New Zealand, where the disease may cause significant growth losses in Douglas-fir (Pseudotsuga menziesii) plantations. In western Oregon, where the pathogen is native, pathogen abundance and disease severity are correlated with mean daily winter temperatures and spring moisture, enabling the development of climate-based disease prediction models. The distribution of P. gaeumannii and severity of Swiss needle cast was surveyed in 16 Douglas-fir plantations throughout New Zealand in 2005. Retention of foliage was assessed in the field and samples of 1- and 2-year-old needles were collected for assessment of P. gaeumannii abundance. Foliage retention and abundance of P. gaeumannii varied across sites. Less colonisation by P. gaeumannii and greater needle retention was found in the South Island. Abundance of P. gaeumannii was found to be positively correlated with August minimum temperature and June average temperature, and showed a similar relationship to winter temperature as observed in western Oregon. These data will be used to derive a disease prediction model for Swiss needle cast in New Zealand that can be used to guide further research and provide short- and long-term disease risk predictions and cost/benefit analyses.

A Climate-Based Model for Predicting Geographic Variation in Swiss Needle Cast Severity in the Oregon Coast Range

ABSTRACT Since the early 1990s, Swiss needle cast disease caused by Phaeocryptopus gaeumannii has been increasing in Douglas-fir plantations in the Oregon Coast Range. Considerable variation in disease severity across the affected area often has been noted. We investigated the influence of site microclimate on fungal colonization as a basis for this variation with a combination of seedling inoculation and field studies. Development of P. gaeumannii ascocarps on inoculated seedlings subjected to mist, irrigation, and shading treatments was followed for 10 months. Contrary to expectations, numbers of ascocarps on foliage were negatively correlated with shade and mist and positively correlated with temperature. Numbers of ascocarps on foliage, site temperature, and leaf wetness were monitored over 5 years at nine field sites in the Oregon Coast Range. Factors most highly correlated with ascocarp abundance were winter mean daily temperature and spring cumulative leaf wetness. Predictive models for disease severity on the basis of these correlations were tested against disease and climate data measured at field sites during 2003-2004. A temperature-based disease prediction model was developed in combination with geographical information systems (GIS)-linked climate databases to estimate disease levels across a portion of the Oregon Coast Range. This model can be used for hypothesis testing and as a decision support tool for forest managers.