Didymascella thujina is an ascomycete fungus in the family Helotiaceae. D. thujina causes cedar leaf blight (also known as Keithia blight or Keithia leaf blight), a leaf disease, on western red cedar (Thuja plicata) and white cedar (T. occidentalis).

Taxonomy and nomenclature The common name of Keithia blight or Keithia leaf blight was derived from the first generic designation for the fungus and remained in use for many years. Pier Andrea Saccardo erected the genus Keithia in 1892 for this fungus,Saccardo PA, 1892. Sylloge Fungorum, 10: 49-50. and in 1903 the genus Didymascella for the same fungus was published as new, twice in the same month.2Maire R, Dumee P, Lutz L, 1901. Prodrome d’une flore mycologique de la Corse. Bulletin de la Société Botanique de France. 1 (series 4): 179-247.Maire R, Saccardo PA, 1903. Sur un nouveau genre de Phacidiacées. Annales Mycologici, 1; 417-419. René Maire in 1905 rejected the generic designation of Didymascella when he followed a suggestion that it was synonymous with Keithia.Maire R, 1905. Notes sur quelques champignons nouveaux ou peu connus. Bulletin de la Société Mycologique de France, 21 : 137-167. In 1927, Maire again took-up the genus Didymascella when it was reported that Keithia was previously used for a genus of flowering plants.Maire R, 1927. Bulletin de la Société d’Histoire Naturelle Afrique du Nord, 18 : 117. The name Keithia thujina remained in use in the literature until 1960 when R. G. Pawsey corrected the name to Didymascella thujina.Pawsey RG, 1960. An investigation into Keithia disease of Thuja plicata. Forestry, 33: 174-186.

Distribution

North America Didymascella thujina occurs on western red cedar (T. plicata) and T. plicata var. atrovirens on the west coast of North America, where it is a significant leaf blight. It also occurs in eastern white cedar (T. occidentalis) in eastern North America, although its effect is insignificant. It also occurs on some varieties of ornamental Thuja.Burmeister P, 1966. Beobachtangen über einige wichtige Pilzkrankheiten an Zierkoniferen im Oldenburgischen Baumschulgebiet. In: de Haas PG, ed. Die Gartenbaumwissenschaft, Bayerischer Landwirtschaftsverlag, Munich, 469-506. Didymascella thujina was found occurring on Port Orford cedar (Chamaecyparis lawsoniana) seedlings in a nursery in Washington, US.Boyce JS, 1961. Forest Pathology. McGraw-Hill Book Company, Toronto.

Didymascella thujina was reported occurring on Atlantic white cedar (Chamaecyparis thyoides) in the eastern US,Adams JF, 1918. Keithia on Chamaecyparis thyoides. Torreya, 18: 157-160. however, this fungus, which occurs on Chamaecyparis species, has since been reclassified as Didymascella chamaecyparisii.Pantidou ME, Korf, RP, 1954. A revision of the genus Keithia. Mycologia, 46: 386-388.Kope HH, 2000. Fungi Canadenses No. 343 Didymascella thujina. Canadian Journal of Plant Pathology, 22: 407-409.

The name Keithia thujina was used by Elias Judah Durand in 1908 for the first record of the disease in the United States on eastern white cedar.Durand EJ, 1909. Transactions of the Wisconsin Academy of Sciences, Arts and Letters, 16; 756. Durand in 1913, further described and illustrated Keithia thujina that was collected from mature trees of eastern white cedar in Wisconsin.Durand EJ, 1913. The genus Keithia. Mycologia, 5: 6-11. Durand felt that the disease only affected the host when environmental conditions favoured epidemics. G. C. Carew noted cedar leaf blight on eastern white cedar in Newfoundland.Carew GC. 1988. A new needle blight disease of Eastern white cedar in Newfoundland. Woody Points Newsletter, 18: 9-10.

From 1912 to 1915 the disease was reported as seriously affecting western red cedar in the western U.S. state of Idaho where it was widely distributed throughout the range of T. plicata, including the adjoining areas of central Oregon, western Montana, and southern British Columbia (B.C.).Weir JR, 1916. Keithia thujina. The cause of a serious leaf disease of Western red cedar. Phytopathology, 6: 360-363. W. A. Porter studied the occurrence and distribution of the disease in western red cedar forests in B.C.Porter WA, 1957. Biological studies on Western red cedar blight caused by Keithia thujina Durand. Canada Department of Agriculture, Forest Biology Division, Interim Report, Victoria, B.C., 25.Wood C, 1986. Distribution maps of common tree diseases in British Columbia. Information Report, BC-X-281, Victoria, B.C.Finck KE, Humphreys P, Hawkins GV, 1989. Field guide to pests of managed forests of British Columbia. Joint Publication. No. 16. FRDA I. Later surveys extended the range of occurrence on western red cedar throughout its coastal and interior ranges in B.C.Foster RE, Wallis GW, 1969. Common tree diseases of British Columbia. Forestry Branch Publications. No. 1245. Department of Fisheries and Forestry, Victoria, B.C., Canada. and Alaska.Anonymous, 1985. Insects and diseases of Alaskan forests. Alaska Region Report Number 181. USDA Forest Service. Cedar leaf blight has been found on both 1 and 2 year-old container-grown western red cedar seedlings in B.C. nurseries,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 and on western red cedar in bare root nurseries in California.Frankel SJ, 1990. Evaluation of fungicides to control cedar leaf blight on Western red cedar at Humboldt nursery. Forest Pest Management Report. No. 90-01. USDA Forest Service, Pacific Southwest Region, 4.

Europe Cedar leaf blight has been introduced into Europe probably being carried on western red cedar imported from North America.Peace JR, 1955. Observations on Keithia thujina and on the possibility of avoiding attack by growing Thuja in isolated nurseries. Report on Forest Research. Forestry Commission, London, 144-148. The first European records were from Ireland where the disease destroyed nursery-grown T. plicata.Pethybridge GH, 1919. A destructive disease of seedling trees of Thuja gigantea Nutt. Quarterly Journal of Forestry, 13: 93-97.Forbes AC, 1920. Occurrence of Keithia thujina in Ireland. The Gardeners’ Chronicles, 68: 228-229.Forbes AC, 1921. Keithia thujina in Ireland. Quarterly Journal of Forestry, 15: 73-75. Soon after its discovery in Ireland the disease was found to be well established in EnglandLoder EG, 1919. Keithia thujina at Leonardslee. Quarterly Journal of Forestry, 13: 287.Miles AC, 1922. Keithia on Thuya plicata. The Gardeners’ Chronicles, 73: 353.Boyce JS, 1927. Observations on forest pathology in Great Britain and Denmark. Phytopathology, 17: 1-18. and Scotland.Alcock NL, 1928. Keithia thujina Durand: A disease of nursery seedlings of Thuja plicata, Scottish Forestry Journal, 42: 77-79.Laing EV, 1929. Notes from the Forestry Department, Aberdeen University. Scottish Forestry Journal, 43: 48-51.Wilson M, 1937. The occurrence of Keithia tsugae in Scotland. Scottish Forestry Journal, 51: 46-47. Later, cedar leaf blight was reported from the NetherlandsPoetern van N, 1931. Verslag over de werksamheden van den plantenziektenkundigen dienst in het jaar 1930. Meded. Plantenziektenkdg, Dienst. Wageningen, No. 64. and Denmark, where it was so serious that nurseries curtailed or stopped growing cedar.Buchwald NF, 1936. En ny svampesygdom i Danmark. Didymascella thujina paa Thuja plicata. Dansk Skovforenings Tidsskrift, 21: 51-59.Ferdinandsen NC, Jorgensen CA, 1938. Skovtraernes Sygdomme, Copenhagen, 181-182. Cedar leaf blight continued to spread to Norway,Jorstad J, Roll-Hasen F, 1943. Melding om sykdommer pa skogtraes i arene. 1936 - 1941, National Samlinge Rikstrykkeri, Oslo, 25. Belgium,Boudru M, 1945. La rouille des aiguilles du Thuja géant (Thuja plicata Don.). Bulletin de la Société royale forestiere de Belgique, 52 : 69-75. France,Anonymous, 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. Switzerland, Italy,Vegni G, Ferro G, 1964. Control of Didymascella (Keithia) thujina dieback of Thuja with zineb. Rivista di Patologia Vegetale, Pavia (Ser. III) 4: 171-176. Germany, Poland,Benben K, 1969. Studies on diseases of North American trees acclimatized in Poland. Prace Instytutow I Laboratoriow Badawczych Przemyslu Spozywczego No 373/375: 129-143. Spain,Fernandez-Magan FJ, 1974. New attacks on Thuja in Galician nurseries. Anales del Instituto Nacional de Investigaciones Agrarias, Recursos Naturales, 1 : 187-199. Austria,Pardatscher G, 1977. Planzenschutz bei Gartenkoniferen. (Plant protection with garden conifers). Besseres Obst, 22 : 29-30 + 45-46. Slovakia,Holubcik M, 1978. Moznosti sl’achtenia lesnych drevin na odolnost’ proti biotickym a abiotickym cinitel’om. (Possibilities in the breeding of forest trees for resistance to biotic and abiotic factors). Vedecke prace vyskumneho ustavu lesneho hospodarstva vo zvolene, 26: 213-232. and the Czech Republic.Prihoda A, 1986. Zasychani vetvi zeravu (Thuja). (Die-back of arbor-vitae (Thuja ) branches.) Sbornik UVTIZ, Zahradnictvi, 13: 307-315. In Germany, Peter Burmeister reported that D. thujina likely occurred on Chamaecyparis lawsoniana, but he was unable to confirm this.

Other areas of the world

There is the risk of cedar leaf blight becoming established wherever Thuja species are introduced and grown, as is evidenced by its occurrence on Thuja species introduced into Europe. Thuja has been introduced to other countries, including India, Australia, Chile and Ukraine,Minter DW, 1997. IMI Descriptions of Fungi and Bacteria No. 1334, Didymascella thujina. but at present D. thujina has not been reported as a disease.

Ecology