Presentation on the biology of Chalara ash dieback disease (Hymenoscyphus fraxineus). Presented at the Living Ash Project Workshop, Grassington, North Yorkshire, 8 June 2017.

1. LAP Ash Dieback Workshop
The biology of Hymenoscyphus fraxineus:
identification and reporting of infected trees
Edward Wilson
Silviculturist
Chalara Ash Dieback Workshop
Yorkshire Dales National Park
Town Hall, Grassington, North Yorkshire
08 June 2017
First presented: 18 06 2014
This version: v3.0, 08 06 2017

2. Outline
• Introduction
– Threats to forests
– History of Chalara ash dieback disease spread
• Biology of Hymenoscyphus fraxineus
– Formerly called Chalara fraxinea
• Identification (picture guide)
• Recognising other threats and reporting infected trees

3. Threats to UK Forests
Source: Forestry Commission England 2012
• Climate change
– Summer droughts increasingly likely, especially in South and East
– Extreme rain and flooding events are more likely
– Ecosystem change – especially ground plants
• Pests and diseases
– Native and exotic
• Low Resilience of Existing Forest Resources
– Low number of productive species
• England – Conifers > 5 species = 88% of area
• England – Broadleaves > 5 species = 72% of area
– Monoculture stands are most common

4. 25th July 2012
Which tree species to plant for a changing
environment
Biosecurity of Trees in Britain: Chalara ash dieback disease
is only the latest on a growing list of nasty pests/pathogens
Source: Forestry Commission 2012

5. 2010 2011
2005
20062002
2009
2003
2002
2011
2012
2012
Decade of Contagion?
Source: Barnaby Wylder 2013

6. History of Hymenoscyphus fraxineus
(formerly Chalara fraxinea)
Date Event/Comment
1992 New lethal disease of ash observed in Poland
1992 - Spread to other regions in Europe; causal agent unclear
Early 2000s A Chalara fungus isolated from many infected trees
2006 Asexual state of the fungus identified and named Chalara
fraxinea
Sexual state thought to be Hymenoscyphus albidus, a wide-
spread and previously non-lethal fungus on ash
2010 Molecular research later confirmed the sexual state is a new
species, Hymenoscyphus pseudoalbidus
May 2014 Revised nomenclature for the fungus has led to new name,
Hymenoscyphus fraxineus

7. Ash dieback disease – Chalara fraxinea
Natural range of ash (Fraxinus excelsior) in Europe
Dates indicate the spread of infection across Europe, with the earliest
cases being confirmed in Poland (1992). Map; EUFORGEN
2012

8. Source: Barnaby Wylder, Forestry Commission 2012
Ash Dieback in Denmark

9. Photo: Mari Jonsson,
Swedish University of Agricultural Sciences
Ash Dieback in Sweden

10. Chalara ash dieback in Europe –
Hymenoscyphus fraxineus
 Vascular wilt fungus
 Pleomorphic (two stage life cycle)
 Emerged as an entirely new
disease in Europe in the 1990s
 Initially cause was unknown –
frost and drought both implicated
in dieback symptoms
 Early impact Poland, Lithuania,
Latvia, then Scandinavian
countries
 Some countries 60-90% ash affected
eg Denmark since 2009.
 Despite impact & spread, not
designated as quarantine
organism
Source: Forestry Commission

11. There appears to be variation among Fraxinus spp.
in resistance or tolerance to Hymenoscyphus fraxineus
Highly susceptible
Fraxinus excelsior
Fraxinus angustifolia
Fraxinus niger
Moderately susceptible
Fraxinus ornus
Fraxinus pennsylvanica
Least susceptible
Fraxinus americana
Fraxinus mandschurica

12. Chalara Ash Dieback Disease
(Hymenoscyphus fraxineus)
• February 2012
– consignment of seedlings
from Netherlands to the
UK found to be infected
with Hymenoscyphus
fraxineus
• October 2012
– Fera confirmed first cases
in “wider environment”
– Note: now thought likely
that the disease arrived in
the UK at an earlier datePhoto: Forestry Commission 2012

13. • November 2012 –
– Cobra Committee Meets
– Rapid action national survey
– Recognition of 2 possible routes
of disease transfer to the UK:
• airborne from western Europe
• Importation of infected seedlings
– Tree Health surveys initiated
• (FC staff and trained contract
surveyors)
Photo: Forestry Commission 2012
Chalara Ash Dieback Disease
(Hymenoscyphus fraxineus)

14. Ash in the UK
Source: Forestry Commission 2013
Ash in the UK:
• 142K Ha
• 11 % of broadleaves
• 14 % of standing
broadleaf volume
• Mostly found in mixed
stands

15. Ash Dieback Locations
6 November 2012
Source: Forestry Commission
Wider Environment
Newly Planted/Nurseries

16. Source: Forestry Commission
Ash Dieback Locations
22 November 2012
Wider Environment
Newly Planted/Nurseries

17. Source: Forestry Commission
Ash Dieback Locations
28 May 2013
Wider Environment
Newly Planted/Nurseries

18. Source: Forestry Commission
Ash Dieback Locations
11 November 2013
Wider Environment
Newly Planted/Nurseries

19. Source: Forestry Commission
Ash Dieback Locations
16 June 2014
Wider Environment
Newly Planted/Nurseries

20. Confirmed reports of Chalara ash dieback (Hymenoscyphus fraxineus) in the UK
1 November 2012 to 6 October 2014
Data: Forestry Commission 2012-2014
Graphic: AshStat/Silviculture ResearchInternational 2014www.silviculture.org.uk
D J F M AN M J J A S O N D J F M A M J A SJ O
2012 2013 2014
0
100
200
300
400
500
600
700
800
900
0 100 200 300 400 500 600 700
CumulativeConfirmedReports
Days from Start of Outbreak
Nursery Sites Recently Planted Sites
Wider Environment Total

21. Ash Dieback Locations
03 August 2015
After October 2014, the Forestry
Commission adopted a new
approach to reporting the location
of infected areas, based on timing
of confirmed site(s) within 10 km
grids.
Note: The map reflects both the
spread of infection, and the
effectiveness of monitoring and
detection.

22. LATEST SITUATION
Ash Dieback Locations
03 April 2017
After October 2014, the Forestry
Commission adopted a new
approach to reporting the location
of infected areas, based on timing
of confirmed site(s) within 10 km
grids.
Note: The map reflects both the
spread of infection, and the
effectiveness of monitoring and
detection.

23. Proposed Map of
Important Ash Locations
Source: Interim Chalara Control Plan, Defra 2012
Areas with widespread Chalara
infection and where the
disease was first established in
the wider environment.
Ash remains an important
feature in the NW and North
Yorks landscape and within
woodland ecosystems.

24. The progress and spread of Chalara dieback of ash is most advanced in Suffolk and Norfolk.
Here natural regeneration established from 2005 is now infected and there is significant
mortality. This site is being monitored to see if there are any resistant trees.
Suffolk Wildlife Trust, Suffolk. Photo: E. R. Wilson 11 August 2015

25. The progress and spread of Chalara dieback of ash is most advanced in Suffolk and Norfolk. Here a group
of pole-stage trees has largely died with a few specimens dying back at a slower rate.
Pound Farm, Woodland Trust, Suffolk. Photo: E. R. Wilson 11 August 2015

26. Anatomy of an ash leaf
Compound leaf
Leaflet
Blade
Midrib
Rachis
Petiolule
Petiole
Photo: E. R. Wilson 2013

27. Model for the invasion and spread strategy
of H. fraxineus in the woody sprout
1. Ascospore state
2. Spore germination or initial mycelium (leaves and petioles)
3. Spread inside wood (longitudinal: pith, vessels and fibres; radial: rays)
4. Cambium and bark necrosis (l) as well as comparable stage after natural infection in the host (r).
Source: Schumacher 2011

28. Ash dieback – a foliar disease
Images courtesy of I Thomsen and L McKinney
Image Stina Bengtsson
Lifecycle of Hymenoscyphus fraxineus
H. fraxineus fruit
bodies on fallen ash
rachises produce
ascospores

29. Ascocarps (fruiting bodies) on the rachis of a decaying ash
leaf from the previous growing season.
11 August 2015, Pound Farm, Suffolk. Photo: E. R. Wilson

30. Spore release of Hymenoscyphus fraxineus
Spore numbers at night Spore numbers at 5am Spore numbers at 7am
Work of Halvor Solheim, Volkmar Timmermann & Isabella Berja, Skog og Landskap, Norway
Early in the morning peaking between 6-8 am during summer

31. Spotting Chalara ash dieback
• Check ash plantations and
woodlands regularly during the
growing season for signs of
Chalara ash dieback disease
• Look for:
– leaf wilting and premature
browning in the growing
season
– Shoot dieback and epicormic
sprouting
– Characteristic diamond-
shaped lesions on stems at
branch unions
• Check current guidance for
disease signs and symptoms – see
www.forestry.gov.uk/chalara
Photo: E. R. Wilson 2014
Photo: E. R. Wilson 2014Photo: Forest Research

32. Signs of disease
Source: Barnaby Wylder, Forestry Commission 2012Source: Forest Research
Diamond-shaped lesions at branch unions Rapid dieback of branches and stems

33. Source: Forestry Commission
Wilting leaves from early summer onwards Fruiting bodies on rachis of decaying leaves
Signs of disease

34. Trace Forward: Recently planted seedling showing
signs of ash dieback disease (Hymenoscyphus fraxineus).
Note 1. dieback on shoots 2. lesions at branch unions 3.
epicormic/adventitious shoot development in current year Photo: Sharon Rodhouse 2012

35. Early signs of ash dieback disease (Hymenoscyphus fraxineus) on young coppice shoots,
Frithy Wood, Suffolk (Green Light Trust). Photo: E. R. Wilson 17 June 2014

36. Dieback on shoots (2013) and wilting leaves (2014), signs of ash dieback disease
(Hymenoscyphus fraxineus), Frithy Wood, Lawshall, Suffolk. Photo: E. R. Wilson 17 June 2014

37. Dieback on shoots of pole-stage ash. Note the different pattern of dieback on adjacent trees.
Golden Wood (Green Light Trust), Lawshall, Suffolk. Photo: E. R. Wilson 17 June 2014

38. Different patterns of ash dieback on adjacent trees, Frithy Wood (Green Light Trust), Lawshall, Suffolk.
At advanced stages of infection trees often succumb due to secondary pathogens, especially honey
fungus (Armillaria spp.). Photo: E. R. Wilson 17 June 2014

39. Where there are high
spore densities it is
possible to see basal
lesions associated with
direct infection of the
stem.
Lesions due to
Hymenoscyphus
fraxineus on the
stem of pole-stage
ash
Photo: J. Clark 2014

40. Photo: E. R. Wilson 2013
Other things we need to be aware of with Ash trees
Ash tress by the River Eamont, Cumbria
There are two ash trees in this picture – one bearing seed (Tree 1 – FEMALE) and the other
not (Tree 2 – MALE). Remember ash keys (samaras) are borne in clusters through winter and
should not be confused with signs of dieback..
Tree 1
Tree 2

41. There is often significant variation in flushing dates
Two veteran ash trees in Cumbria, 19 May 2014
(approximately 200 m apart)
Photos: E. R. Wilson 2014

42. Dasineura fraxini
the ash midrib gall midge Photo: E. R. Wilson 2013

43. Photograph courtesy of Nigel Straw, Forest Research
The ash bud moth Prays fraxinella,
is a native micromoth.
Ash key gall caused by the
eriophyid mite Aceria fraxinivora.
Source: OPAL

44. Nectria canker is caused by the
fungus Neonectria galligena.
Emerald Ash Borer (Agrilus
planipennis) is currently NOT
present in UK.
Source: OPAL

45. Emerald ash borer on leaf of American white ash, Fraxinus americana. Toronto, Ontario,
Canada. Photo: E. R. Wilson 17 June 2015
Emerald Ash Borer – Most Unwanted!
Not present in the UK at present time; risk of future introduction

46. Emerald ash borer. Toronto, Ontario, Canada. Photo: E. R. Wilson 17 June 2015
Emerald Ash Borer – Most Unwanted!
Not present in the UK at present time; risk of future introduction

47. Emerald ash borer damage to American white ash, Fraxinus americana. Toronto, Ontario,
Canada. Photo: E. R. Wilson 17 June 2015

48. Emerald ash borer damage to American white ash, Fraxinus americana. Note the larval frass
trails in what was the cambium layer inside the bark. Toronto, Ontario, Canada.
Photo: E. R. Wilson 17 June 2015

49. Emerald ash borer damage to American white ash, Fraxinus americana.
Scarborough neighbourhood, Toronto, Ontario, Canada. Photo: E. R. Wilson 17 June 2015

50. Emerald ash borer damage to American white ash, Fraxinus americana.
Scarborough neighbourhood, Toronto, Ontario, Canada. Photo: E. R. Wilson 17 June 2015

51. A high profile public awareness and education programme is being delivered by the
Forestry Department at the Town of Oakville. Here we see adverts placed on local buses.
Town of Oakville, Ontario, Canada. Photo: E. R. Wilson 16 June 2015

52. The Forestry Department at the Town of Oakville is highly engaged with researchers and
collecting data on EAB population dynamics, in partnership with other agencies, including
the Ontario Ministry of Natural Resources and the Canadian forest Service. Here we see a
pheromone trap being installed in an ash tree.
Town of Oakville, Ontario, Canada. Photo: E. R. Wilson 16 June 2015

53. Summary
• Forest pests and diseases are a major issue in Britain and elsewhere
(Globalisation, Climate change)
• Chalara ash dieback disease has spread across the range of ash in Britain
• Vascular wilt fungus with aerial ascospores, difficult to treat/control
• Signs and Symptoms (lesions, leaf wilt, epicormics and evidence of
ascospores on rachi)
• Many other threats to ash, non-lethal and lethal
– Vigilance is important with respect to potential introduction of
emerald ash borer
• Public engagement is important in managing tree health issues and newly
introduced threats
• Further Information: https://www.forestry.gov.uk/pestsanddiseases
• Reporting tree health issues: www.forestry.gov.uk/treealert

54. livingashproject.org.uk
Project partners:

55. LAP Ash Dieback Workshop
Acknowledgements
My thanks to the following colleagues: Ben Jones and Barnaby Wylder, Forestry
Commission England; Joan Webber, Forest Research; Kate Holl, Scottish Natural
Heritage; Mari Jonsson, Swedish University of Agricultural Sciences; Tom Brown,
Green Light Trust; Jo Clark, Earth Trust; Sharon Rodhouse, Sylvatic Ltd
Further Information
Edward Wilson
Email: ted.wilson@rfs.org.uk
First presented: 18 06 2014
This version: v3.0, 08 06 2017