Chalara fraxinea

Ash dieback

Why: A new disease causing tree mortality has increasingly been observed in European countries on ash trees (Fraxinus excelsior) during the last ten years. The first studies revealed the presence of a pathogenic fungus which was described as a new species, Chalara fraxinea. Because ash dieback could represent a serious threat to forest, amenity and nursery ash trees, the EPPO Secretariat decided to add C. fraxinea to the EPPO Alert List in 2007. Further studies carried out in 2008 in Poland revealed that C. fraxinea was the anamorph of an already described species, Hymenoscyphus albidus, which is considered as non-pathogenic, native, and widespread in Europe. Therefore, the emergence of a new disease caused by this species is difficult to explain, and it is acknowledged that further studies are needed to better understand the taxonomy and biology of the H. albidus/C. fraxinea complex.

Pictures were kindly provided by Prof. H. Solheim (Norwegian Forest
and Landscape Institute, Aas), more can be viewed on the EPPO gallery

Where:
EPPO region: Austria, Czech Republic, Finland, France, Germany, Hungary, Italy, Lithuania, Norway, Poland, Slovenia, Sweden (C. fraxinea has been identified in these countries). On the basis of symptoms, the disease has also been observed in: Denmark, Estonia, Latvia, and Switzerland.

On which plants: Fraxinus excelsior (European ash)  and F. angustifolia (narrow-leafed ash). No data is available on the susceptibility of other Fraxinus species.

Damage: Initially, small necrotic spots (without exudate) appear on stems and branches. These necrotic lesions then enlarge resulting in wilting, dieback of branches and particularly in the death of the top of the crown. The disease is often chronic but can be lethal. Ash dieback has been observed not only on forest trees but also in urban areas (parks and gardens) and in nurseries.

Dissemination: Data is lacking on the biology of C. fraxinea. It was isolated from diseased twigs and branches, as well as in dead roots of living ash trees.

Pathway: Although data is lacking on the biology of the fungus, it seems likely that plants for planting and wood of F. excelsior could be pathways for spreading the disease over long distances.

Possible risks: Fraxinus are widely grown across the EPPO region both for forestry and amenity purposes. Although data is still lacking on the exact role of C. fraxinea in ash dieback, EPPO member countries should be warned that ash dieback is emerging in Europe and that there may be a risk in moving diseased F. excelsior plants across the region without any precaution. Further studies are obviously needed on the etiology of ash dieback, its geographical distribution and economic impact.

Source(s)
Anonymous (2008) La lettre du DSF no. 37 – Décembre 2008. Département de la Santé des Forêts (FR), 12 pp.
Anonymous (2009) La lettre du DSF no. 38 – Juin 2009. Département de la Santé des Forêts (FR), 9 pp.
Anonymous (2009) La lettre du DSF no. 39 – Décembre 2009. Département de la Santé des Forêts (FR), 9 pp.
Halmschlager E, Kirisits T (2008) First report of the ash dieback pathogen Chalara fraxinea on Fraxinus excelsior in Austria. New Disease Reports, Volume 17, February 2008 - July 2008. http://www.bspp.org.uk/ndr/july2008/2008-25.asp
Ioos R, Kowalski T, Husson C, Holdenrieder O (2009) Rapid in planta detection of Chalara fraxinea by a real-time PCR assay using a dual-labelled probe. European Journal of Plant Pathology (in press).
Jankovský L, Holdenrieder O (2009) Chalara fraxinea ash dieback in the Czech Republic. Plant Protection Science 45(2), 74-78 (abst.).
Kirisits T, Matlakova M, Mottinger-Kroupa S, Halmschlager E, Lakatos F (2010) Chalara fraxinea associated with dieback of narrow-leafed ash (Fraxinus angustifolia). Plant Pathology 59(2), p 411.
Kowalski T (2006) Chalara fraxinea sp. nov. associated with dieback of ash (Fraxinus excelsior) in Poland. Forest Pathology 36(4), 264-270.
Kowalski T, Holdenrieder O (2008) Pathogenicity of Chalara fraxinea. Forest Pathology 38(6), 1-7.
Kowalski T, Holdenrieder O (2009) The teleomorph of Chalara fraxinea, the causal agent of ash dieback. Forest Pathology (in press).
NPPO of Finland (2008-10).
NPPO of Italy (2009-11).
NPPO of Slovenia (2009-01).
Ogris N, Hauptman T, Jurc D, Floreancig V, Marsich F, Montecchio L (2010) First report of Chalara fraxinea on common ash in Italy. Plant Disease 94(1), p 133.
Schumacher J, Wulf A, Leonhard S (2007) [First record of Chalara fraxinea T. Kowalski sp. nov. in Germany – a new agent of ash decline.] Nachrichtenblatt des Deutschen Pflanzenchutzdienstes 59(6), 121-123 (in German).
Szabó I (2008) [Dieback of common ash (Fraxinus excelsior) caused by Chalara fraxinea.] Növényvédelem 44(9), 444-446 (in Hungarian).
Personal communication with Dr Bjørn Økland, Norwegian Forest and Landscape Institute, Ås, Norway (2008-08).
Personal communication with Prof. Halvor Solheim, Norwegian Forest and Landscape Institute, Ås, Norway (2008-09).
INTERNET (last retrieved in 2007-09)
Forest & Landscape Denmark. Ash dieback in Denmark. http://en.sl.life.ku.dk/forskning/fagdatacenterskov/skovsundhed/skader/asketoptoerre.aspx
Institut fédéral de recherches sur la forêt, la neige et le paysage WSL, Birmensdorf (CH). Meier F, Engesser R, Forster B, Odermatt O, Angst A (2008) Protection des forêts – Vue d’ensemble 2007. http://www.wsl.ch/forschung/forschungsunits/walddynamik/waldschutz/wsinfo/fsueb/fsub07f.pdf
Mattilsynet. Regulations of 8 September 2008 concerning measures against Chalara fraxinea. http://www.mattilsynet.no/english/plant_health/regulations_of_8_september_2008_concerning_measures_against_chalara_fraxinea_63077
NAPPO – Pest Alert System. Chalara fraxinea Kowalski - Intensive dieback of European ash in Poland associated with a newly described fungal species, Chalara fraxinea. http://www.pestalert.org/viewNewsAlert.cfm?naid=26
Nordic Forest Research Cooperation Committee. Ash decline in Nordic and Baltic countries. http://www.metla.fi/org/pathcar/ash-decline.htm
Research and Training Centre for Forests, Natural Hazards and Landscape (BFW) Actual situation of dieback of ash in Austria by TL Cech and U Hoyer-Tomiczek. http://bfw.ac.at/400/pdf/fsaktuell_40_3.pdf
Norwegian Institute of Forestry and landscape. Ash dieback. http://www.skogoglandskap.no/nyheter/2008/askens_endelikt (in Norwegian).
Ash dieback and premature leaf shedding in Austria by TL Cech. http://bfw.ac.at/400/pdf/fsaktuell_37_8.pdf

EPPO RS 2007/179, 2008/128, 2008/180, 2008/181, 2008/182, 2008/183, 2008/199, 2009/066, 2009/131, 2009/132, 2010/018, 2010/035, 2010/115, 2010/116