Didymascella thujina (cedar leaf blight)
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Means of Movement and Dispersal
- Seedborne Aspects
- Plant Trade
- Impact Summary
- Economic Impact
- Environmental Impact
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Didymascella thujina (E.J. Durand) Maire 1927
Preferred Common Name
- cedar leaf blight
Other Scientific Names
- Keithia thujina E.J. Durand 1913
International Common Names
- English: Keithia blight; Keithia leaf blight; needle blight: western red cedar
- French: brunissure des aiguilles du Thuya; rouille des aiguilles du Thuya
Local Common Names
- Germany: Keithia-Krankheit: Lebensbaum; Laubbraeune: Lebensbaum; Schuppenbraeune: Lebensbaum; Thujablattbräune
- DIDSTH (Didymascella thujina)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Fungi
- Phylum: Ascomycota
- Subphylum: Pezizomycotina
- Class: Dothideomycetes
- Subclass: Dothideomycetidae
- Order: Capnodiales
- Family: Mycosphaerellaceae
- Genus: Didymascella
- Species: Didymascella thujina
Notes on Taxonomy and NomenclatureTop of page
DescriptionTop of page
DistributionTop of page
D. thujina is native to North America where it was first found in 1908 on mature trees of eastern white cedar (Thuja occidentalis) in Wisconsin, USA (Durand, 1913). Durand felt that the disease only affected the host when environmental conditions favoured epidemics. From 1912 to 1915 the disease was reported as seriously affecting western red cedar (Thuja plicata) in the western US state of Idaho (Weir, 1916) where it was widely distributed throughout the range of T. plicata, including the adjoining areas of central Oregon, western Montana and southern British Columbia, Canada. Porter (1957) studied the occurrence and distribution of the disease in western red cedar forests in British Columbia. More recently, the disease been found on western red cedar throughout its coastal and interior ranges in British Columbia (Foster and Wallis, 1969; Wood, 1986; Finck et al., 1989) and Alaska (Anon., 1985). Carew (1988) noted Keithia blight on eastern white cedar in Newfoundland, Canada. Keithia blight has been found on 2-year-old, container-grown, western red cedar (Dennis and Sutherland, 1989) and western red cedar transplants in coastal nurseries in British Columbia and on western red cedar in bare-root nurseries in California (Frankel, 1990).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 10 Jan 2020
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Netherlands||Present, Widespread||Introduced||Invasive||Original citation: van Poetern, 1931|
|Spain||Present||Introduced||Invasive||Original citation: Fernandez-Magan, 1974|
|United Kingdom||Present, Localized||Introduced||Invasive|
|Canada||Present||Present based on regional distribution.|
|-British Columbia||Present, Widespread||Native||Invasive|
|-New Brunswick||Present, Widespread||Native||Invasive|
|-Newfoundland and Labrador||Present, Widespread||Native||Invasive|
|-Prince Edward Island||Present, Widespread||Native||Invasive|
|United States||Present||Present based on regional distribution.|
|-Alaska||Present, Widespread||Native||Invasive||Original citation: Anon. (1985)|
|-New York||Present, Widespread||Native||Invasive|
History of Introduction and SpreadTop of page
Risk of IntroductionTop of page
HabitatTop of page
Habitat ListTop of page
|Terrestrial||Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Protected agriculture (e.g. glasshouse production)||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Managed forests, plantations and orchards||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Rail / roadsides||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Urban / peri-urban areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Natural forests||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Riverbanks||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Wetlands||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Cold lands / tundra||Present, no further details||Harmful (pest or invasive)|
|Littoral||Coastal areas||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page
SymptomsTop of page
List of Symptoms/SignsTop of page
|Leaves / abnormal colours|
|Leaves / abnormal colours|
|Leaves / necrotic areas|
|Leaves / necrotic areas|
|Whole plant / seedling blight|
|Whole plant / seedling blight|
Biology and EcologyTop of page
Pathogen-produced toxins may have a role in the killing of host tissue (Anon., 1967). A physiological change in T. plicata appears to account for an increase in blight resistance when trees are 4 or 5 years old (Soegaard, 1969). The consequence of cedar leaf blight infection of the foliage of mature cedar trees (>50 year of age) is unknown; mortality is rare and loss of incremental growth may be the chief result. However, cedar leaf blight may be a pioneering fungal pathogen that induces stress on the host tree allowing a succession of further disease-causing organisms.
The disease requires two growing seasons before the symptoms become apparent (Phillips and Burdekin, 1982; Sutherland et al., 1995). In natural stands of its host, infection occurs during one growing season and apothecial formation occurs during the next growing season. When apothecial formation occurs in the first year, such as 1-year-old seedlings grown in a reforestation nursery, infection and subsequent disease expression is often restricted to the juvenile needles on the stem and, in some cases, to the lower branches (Kope and Sutherland, 1994). It is rare for apothecial formation to occur in the same growing season as infection.
New infections are initiated by ascospores and the disease is spread only by ascospores. These spores are released during two periods in a growing season in the Pacific Northwest of North America, in the spring from April to the end of June, and in the autumn from late September to early November (Kope and Sutherland, 1994). More ascospores are released during the spring season release period than during the autumn season release period, thus an ascospore release cycle can be predicted throughout a growing season. In Denmark, Søegaard (1969) found two periods of ascospore discharge: one in early June and another from late September to early October. In England, UK, ascospores are most abundant from June to July and from September to October (Phillips, 1967; Burdekin, 1968).
Ascospore germination forms an infection peg, which penetrates the host mesophyll cells mechanically rather than via stomata (Porter, 1957; Pawsey, 1960; Søegaard, 1969). Although the mycelium spreads throughout the mesophyll, it does not penetrate the vascular bundles and its growth is limited to cells of an individual infected leaflet (Pawsey, 1960). At temperatures above 15°C, the affixed ascospores can germinate within 12 hours and penetrate the host leaflet. The germination rate drops sharply below 15°C, but affixed ascospores can remain quiescent. Fungal growth within the leaflet requires the accumulation of approximately 1200 growing degree days above 5°C in a glasshouse environment (Kope and Trotter, 1998b). Ordinarily, in natural stands of its host, the disease cycle occurs over two growing seasons with an accumulation of degree days during the first growing season, overwintering, then a further accumulation of degree days to approximately 1480 (Kope and Trotter, 1998b) before apothecia form.
When the apothecia are fully mature and become wet, they swell and break through the leaf epidermis. The swelling pushes up the fruiting body and exposes it to the circulating air. As the apothecia dries in the circulating air, the ascospores are forcibly released. At temperatures between 10 and 20°C, ascospores can be released for up to 6 hours; at temperatures below 10°C, very few ascospores are released over a shorter period. Almost no ascospore release occurs below 5°C. Ascospore release stops when the epidermal scale folds over and covers the fruiting body until the next episode of wetting. A repeating cycle of wetting and drying of apothecia (i.e., irrigation) at temperatures between 10 and 20°C will cause the release of all viable ascospores during 5 days. Should intervals between wettings be prolonged, ascospores within apothecia can remain viable for up to 14 days. Ascospore release will recur once the apothecia are rewetted. However, apothecia and ascospores do not last indefinitely and during a prolonged dry period they will be colonized by other microorganisms such as Phoma sp., thus destroying the ascospores and apothecia. If the apothecia are continually wet, ascospore release can continue until exhausted, a period of 2 days. At cooler temperatures the ascospores and fruiting bodies remain viable but will be colonized by other fungi. Ascospores are not released until the temperature reaches 5°C.
Means of Movement and DispersalTop of page
Seedborne AspectsTop of page
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Leaves||fruiting bodies||Yes||Yes||Pest or symptoms usually invisible|
|Seedlings/Micropropagated plants||fruiting bodies; spores||Yes||Yes||Pest or symptoms usually invisible|
|True seeds (inc. grain)||spores||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
|Fisheries / aquaculture||None|
ImpactTop of page
Economic ImpactTop of page
Environmental ImpactTop of page
DiagnosisTop of page
Detection and InspectionTop of page
Similarities to Other Species/ConditionsTop of page
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.Introduction
The same conditions that make nursery production of seedlings successful - high densities, favourable temperatures and moisture, and intensive crop management techniques - are also ideal for the Keithia leaf blight fungus. Healthy trees result when pest management is integrated with other aspects of nursery culture throughout the crop cycle.
Numerous studies have been conducted using fungicides to control Keithia blight on nursery seedlings. As early as 1916, Weir found that a soap-Bordeaux mixture provided protection when applied at 10-day, or shorter, intervals. In the UK, several fungicides were tested against Keithia blight. Inconclusive results were obtained with a lime sulphur mixture (Peace, 1955), probably because the material was short lived. Pawsey (1962b), reporting on trials conducted over 10 years, found that a high degree of resistance to various fungicides developed but some protection was provided by copper-based fungicides. Burdekin (1969) found that the fungicide cycloheximide and its derivatives were effective against blight. Although there was some phytotoxicity with cycloheximide, there was none with oxime, semicarbazone and other acetate derivatives (Pawsey, 1964; Phillips, 1965, 1966). Further experiments (Pawsey, 1964; Phillips, 1965, 1966) demonstrated that if fungicides were applied once per month in March, April and June, all concentrations of cycloheximide derivatives reduced blight severity. Additional applications in the summer and autumn continued to reduce blight levels, but the cycloheximide derivatives were not systemic and had no effect on blight reduction the following spring. Fungicides that were ineffective against the disease included zineb and maneb (Pawsey, 1964), captan (Burdekin, 1968), fentin hydroxide, diodine acetate, diathion, streptomycin and an organomercurial fungicide (Phillips, 1967). In follow-up studies, Burdekin and Phillips (1971) found that one application of cycloheximide in March, another in April, and sometimes again in June, gave the best disease control, probably because spore germination was inhibited, which limited the build up and spread of Keithia blight. In France, Boudier (1983) tested several fungicides against Keithia blight. Two application schedules were tested, i.e., one where the fungicides were applied every 3 weeks from June to October and another in which they were applied every 3 weeks from September to October. At both application schedules he found that the systemic triadimenol was the most effective in protecting seedlings into the next growing season whereas fixed copper was ineffective. The efficacy of fixed copper, benomyl and triadimefon was determined against blight on 1-year-old western red cedar in a Californian bareroot nursery (Frankel, 1990). Keithia blight was least severe on seedlings sprayed monthly from March through November with the systemic triadimefon. A subsequent trial demonstrated that three triadimefon applications in April, May and June, or in April, June and August controlled blight (Frankel, 1991, 1992).
More recently, Kope and Trotter (1998a) tested two fungicides for the control of cedar leaf blight in nurseries. Mancozeb is a foliar spray that must directly contact the target fungus to be effective. Its protective value is short-lived, thus the seedlings must be sprayed bi-weekly, at the recommended rate, for the entire growing season (12-14 applications). Propiconazole is a systemic fungicide that is absorbed through the leaves and translocated throughout the seedling. Propiconazole can be used to protect 1+0 or older container-grown or bare-root western red cedar seedlings. Applied at the recommended rate and at a frequency of once every 4 weeks to a maximum of six times within a growing season, propiconazole is effective in the control of Keithia leaf blight of western red cedar. If control of cedar leaf blight is to be achieved through fungicides alone, they must be applied early and throughout the growing season of 1-year-old seedlings and the full growing season of 2-year-old seedlings. The effect of the fungicide is to damage ascospores that are on the leaflet surface and drift into the growing areas during a spring release period and the newly forming fruiting bodies and their ascospores forming in the autumn on the foliage.
Various modifications of cultural practices have been tried for the control of cedar leaf blight. In the UK, western red cedar seedlings were grown in nurseries isolated from known sources of inoculum, but the results were inconclusive (Peace, 1958). Another suggestion was to grow Thuja in isolated nurseries (Pawsey, 1962a). Thuja would be raised from seed at isolated nurseries with a periodic clearance of all cedar stock before resowing. This was partly successful, but some outbreaks of Keithia blight occurred (Burdekin and Phillips, 1971). Growing bare-root nursery or transplant cedar at reduced densities (seedlings per unit area), e.g., to decrease humidity within the canopy, has provided some measure of blight control (Keatinge, 1948; Evans, 1950; Penistan, 1966). Growing cedar as a mixture with other species, both in seed and transplant beds, has also given some control of the disease (Peace, 1955).
Resistance to Keithia blight is known in Thuja. Søegaard (1954, 1956) inoculated both cuttings from a mature western red cedar tree and seedlings from the same tree, and showed that the cuttings were more resistant than the seedlings. Søegaard (1956, 1969) also determined that resistance is the result of a recessive gene in T. plicata. Crossing Thuja plicata with a Japanese species, Thuja standishii, where resistance was dominant, resulted in a 1:1 ratio of resistant to susceptible offspring. Søegaard suggested that cuttings could be produced from such hybrids.
On the basis of results over four growing seasons, Burmeister (1966) listed the disease ratings of several varieties of T. plicata, T. occidentalis and T. standishii. Two varieties of T. plicata, 'Fastigata' and 'Auerovariegata' were highly susceptible, whereas T. standishii was highly resistant. Porter (1957), in attempting to explain the variation in blight severity in British Columbia, Canada, collected T. plicata cuttings and inoculated some in the field and others in the laboratory. No resistance was found, regardless of host origin, inoculation site or technique. On the basis of these results, Porter (1957) concluded that the microclimate is mainly responsible for differences in blight severity.
Older infected cedar stock or infected cedar trees surrounding a nursery can provide inoculum and the ascospores can travel through the air. Airborne ascospores can be kept out of cedar-rearing greenhouses by keeping a roof and side walls in place until after the spring ascospore release period (end of June, on Vancouver Island and the lower mainland of North America). This practice directly prevents ascospores from coming in contact with the cedar crop.
Through the summer months of July, August and September, when climatic conditions are warmer and drier, circulating dry air through the crop will decrease the time that foliage remains wet. As the crop matures, foliage density increases and moisture is retained on leaf surfaces, especially the lower branches. Free water is required for the germination and infection of leaves by the Keithia leaf blight fungus. Foliage wetness can be decreased by separating the growing containers to allow more efficient drying out between waterings.
From October through to the end of November, air should be allowed to circulate through the crop, and where possible, seedlings should be protected from the rain. If infection has occurred, fruiting bodies can form and disease spread will be encouraged by the presence of moisture on the infected foliage.
Seedlings held over for growth for another year into the spring are particularly susceptible to Keithia leaf blight infection and expression. Such seedlings must be protected throughout the previous growing season, or disease expression will occur early in the spring. The first signs of the disease are often subtle and overlooked in the early spring and the disease can easily spread. By applying fungicides to the crop in the first growing season and continuing through the second growing season, a disease-free crop of 2+0 western red cedar can be produced.
ReferencesTop of page
Adams JF, 1918. Keithia on Chamaecyparis thyoides. Torreya, 18:157-160.
Anon, 1960. United States Department of Agriculture. Agricultural Handbook, Number 165. Washington, DC, USA: USDA.
Anon., 1953. Notes phytosanitaires. Evolution des maladies des plantes en 1951. Annales de L’institut national de recherche agronomique, serie C (Annales des Épiphyties), 511-515.
Anon., 1985. Insects and diseases of Alaskan forests. Alaska Region Report Number 181. USDA Forest Service.
Boudier B, 1983. Didymascella thujina principal ennemi du Thuya dans l’ouest de la France. Phytoma - Defense des cultures, novembre, 51-56.
Boyce JS, 1927. Observations on forest pathology in Great Britain and Denmark. Phytopathology, 17:1-18.
Buchwald NF, 1936. En ny svampesygdom i Danmark. Didymascella thujina paa Thuja plicata. Dansk Skovforenings Tidsskrift, 21:51-59.
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Burdekin DA, 1969. Needle blight of Western Red Cedar caused by Didymascella thujina. Report on Forestry Research. Forestry Commission, London.
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Carew GC, 1988. A new needle blight disease of Eastern white cedar in Newfoundland. Woody Points Newsletter, 18:9-10.
Dennis J; Sutherland JR, 1989. Keithia Blight. Seed and Seedling Extension Topics. No. 2:1 Province of British Columbia, Ministry of Forests, Victoria, B.C., 15.
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Forbes AC, 1921. Keithia thujina in Ireland. Quarterly Journal of Forestry, 15:73-75.
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Frankel SJ, 1991. Timing and applications of triadimefon (Bayleton) needed for control of cedar leaf blight on Western red cedar at Humboldt nursery. Forest Pest Management Report. No. 91-01. USDA Forest Service, Pacific Southwest Region. 4.
Frankel SJ, 1992. Additional studies on rate and number of Triadimefon (Bayleton 25% WP) applications needed for control of cedar leaf blight on Western red cedar at Humboldt nursery. Forest Pest Management Report. No. 92-02. USDA Forest Service, Pacific Southwest Region, 5.
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Kope HH; Dennis J, 1992. Keithia blight on Western Red Cedar nursery seedlings. Seed and Seedling Extension Topics. No. 5:(l); Province of British Columbia, Ministry of Forests, Victoria, BC 11.
Kope HH; Ekramoddoullah AKM; Sutherland JR, 1998. Analysis of proteins of disease-free and Didymascella thujina-infected leaves of western red-cedar (Thuja plicata). Plant Disease, 82(2):210-212; 16 ref.
Kope HH; Sutherland J, 1994. Keithia blight: A review of the disease, and research on container-grown, Western redcedar in British Columbia, Canada. In Proceedings of the second meeting of IUFRO Working Party, S2.07-09 (Diseases and Insects of nurseries).
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Laing EV, 1929. Notes from the Forestry Department, Aberdeen University. Scottish Forestry Journal, 43:48-51.
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Penistan MJ, 1966. Rubbish to seed stand (Western red cedar). Quarterly Journal of Forestry, 60:237.
Pethybridge GH, 1919. A destructive disease of seedling trees of Thuja gigantea Nutt. Quarterly Journal of Forestry, 13:93-97.
Phillips DH, 1965. Needle blight (Didymascella thujina [Dur.] Maire, syn. Keithia thujina Dur.) of Western Red Cedar (Thuja plicata). Report on Forest Research. Forestry Commission, London, 63.
Phillips DH, 1966. Needle blight (Didymascella thujina [Dur.] Maire, Keithia thujina Dur.) of Thuja. Report on Forest Research. Forestry Commission, London, 73.
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Soegaard B, 1969. Resistance studies in Thuja. A, Investigations of resistence to attack by Didymascella thujina (Dur.) Maire in Thuja plicata D. Don and its hybrids with Thuja stadishii (Gord.) Carr. B. Time of flowering and its bearing on the effectivitiy of pollination in Thuja plicata D. Don. Det Forstlige Forsogsvaesen I Danmark, 31(3):279-398 + 14 figs., 12 tbls. [3 pp. of refs.].
Søegaard B, 1956. Leaf blight resistance in Thuja. Yearbook 1956. Royal Veterinary and Agricultural College, Copenhagen, Denmark. 30-48.
Weir JR, 1916. Keithia thujina. The cause of a serious leaf disease of Western red cedar. Phytopathology, 6:360-363.
Wilson M, 1937. The occurrence of Keithia tsugae in Scotland. Scottish Forestry Journal, 51:46-47.
Wood C, 1986. Distribution maps of common tree diseases in British Columbia. Canadian Forest Service, Pacific Forestry Centre, Victoria, British Columbia, Canada. Information Report, BC-X-281.
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Anon, 1960. United States Department of Agriculture. In: Agricultural Handbook, 165 Washington, DC, USA: USDA.
Buchwald N F, 1936. A new fungal disease in Denmark. Didymascella thujina of Thuja plicata. (En ny svampesygdom i Danmark. Didymascella thujina paa Thuja plicata.). Dansk Skovforenings Tidsskrift. 51-59.
Burmeister P, 1966. (Beobachtangen über einige wichtige pilzkrankheiten an zierkoniferen iin Oldenburgischen baumschulgebiet). In: Die Gartenbaumwissenschaft, [ed. by de Haas PG]. Munich, Bayerischer Landwirtschaftsverlag. 469-506.
CABI, Undated. Compendium record. Wallingford, UK: CABI
CABI, Undated a. CABI Compendium: Status inferred from regional distribution. Wallingford, UK: CABI
CABI, Undated b. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI
Holubcik M, 1978. Possibilities in the breeding of forest trees for resistance to biotic and abiotic factors. (Moznosti sl'achtenia lesnych drevin na odolnost' proti biotickym a abiotickym cinitel'om.). Vedecke Prace Vyskumneho Ustavu Lesneho Hospodarstva vo Zvolene. 213-232.
Juronis V, Snieškienė V, Žeimavičius K, Stankevičienė A, 2006. Estimation of Thuja L. genus plants state in Central Lithuania. (Thuja L. genties augalų bu¯klės įvertinimas Vidurio Lietuvoje.). Vagos. 25-33. http://www.lzua.lt/vagos
ContributorsTop of page
18/05/04 Original text by:
Harry H Kope, Resource Practices Branch, British Columbia Ministry of Forests, Lands and Natural Resource Operations, Victoria, BC, Canada
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