Ash Dieback
Chalara fraxinea
Alistair McCracken & Louise Cooke
Applied Plant Science & Biometrics Division
November 2012
Ash
(Fraxinus excelsior)
Chalara dieback of ash
Chalara fraxinea (asexual)
Anamorph of new species
called: Hymenoscyphus
pseudoalbidus (sexual)
Ash Dieback
• The causal agent of dieback of European ash
(Fraxinus excelsior) was first (2006)
described as Chalara fraxinea.
• Study of the teleomorph of C. fraxinea
revealed a species complex but that the
strain causing ash dieback should be reassigned to Hymenoscyphus pseudoalbidus
(2011).
Chalara fraxinea hosts
• Fraxinus excelsior (European Ash)
• F. angustifolia (Narrow-leaved Ash)
• F. nigra (Black Ash)
• F. ornus (Manna Ash / South European Flowering Ash)
• F. pennsylvanica (Green Ash)
• F. americana (White Ash / American Ash)
• F. mandschurica (Manchurian Ash)
Impact
“The disease is particularly prevalent in Denmark where
up to 90 per cent of trees in many locations are infected
and all are expected to die. Chalara ash dieback has
the capacity to inflict on common ash what Dutch elm
disease did to English elm in the 1970s. That is to
essentially wipe out the species as forest, woodland,
amenity and landscape tree in the UK.”
(British and International Greenkeepers Association Ltd. Sept. 2012)
Pathways
• Movement of soil, plants for planting or
wood are possible pathways for longdistance transmission
• Wind-borne spores can move up to 30
km/year
• Plants for planting from known infected
areas are considered to be the likely
means of entry
Spread from plant to plant
• Aerial spread
– Asexual spores are not thought to be an
important means of dissemination
Sexual spores
• Sexually formed spores
(Hymenoscyphus psaudoalbidus) can be
dispersed by wind and would appear to be
the more important means of dispersal
Dispersal rate
• Evidence from Norway has suggested a
potential dispersal rate of 20-30 km/year.
• There is evidence of insect (flies; sapfeeders) dispersing other Chalara spp.
Symptoms
• Symptoms of Chalara fraxinea can be
visible on leaves, shoots and branches
of infected trees
• In severe cases the entire crown shows
leaf loss and dieback
intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior)
Andrej Kunca, National Forest Centre - Slovakia, Bugwood.org
intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior)
Andrej Kunca, National Forest Centre - Slovakia, Bugwood.org
intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior)
intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior)
intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior)
intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior)
intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior)
intensive dieback of ash (Chalara fraxinea) on European ash (Fraxinus excelsior)
Canker caused by Chalara
fraxinea on Fraxinus
Prof. H. Solheim, Norwegian Forest and Landscape Institute,
Aas, Norway
Times of year when symptoms are most likely to be observed
Jan
Leaf
necrosis
Shoot
lesions
Stem
lesions
Fruiting
bodies
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Detection and Diagnosis
• Culturing
Difficult to culture
Very slow growing –
could take 5 – 8
weeks to get a colony
Molecular (PCR)
• Molecular lab is fully set up to examine
plant samples and / or cultures
Thank you