biology of chalara ash dieback disease (june 2017)

LAP Ash Dieback Workshop

The biology of Hymenoscyphus fraxineus:

identification and reporting of infected trees

Edward WilsonSilviculturist

Chalara Ash Dieback WorkshopYorkshire Dales National ParkTown Hall, Grassington, North Yorkshire08 June 2017

First presented: 18 06 2014This version: v3.0, 08 06 2017

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

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

25th July 2012Which 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

2010 2011

2005

20062002

2009

2003

2002

20112012

2012

Decade of Contagion?

Source: Barnaby Wylder 2013

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

Ash dieback disease – Chalara fraxineaNatural 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

Source: Barnaby Wylder, Forestry Commission 2012

Ash Dieback in Denmark

Photo: Mari Jonsson, Swedish University of Agricultural Sciences

Ash Dieback in Sweden

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

There appears to be variation among Fraxinus spp. in resistance or tolerance to Hymenoscyphus fraxineus

Highly susceptibleFraxinus excelsior

Fraxinus angustifolia

Fraxinus niger

Moderately susceptibleFraxinus ornus

Fraxinus pennsylvanica

Least susceptibleFraxinus americana

Fraxinus mandschurica

Chalara Ash Dieback Disease(Hymenoscyphus fraxineus)

• February 2012

– consignment of seedlings from Netherlands to the UK found to be infected

with Hymenoscyphusfraxineus

• 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

• 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)

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

Ash Dieback Locations6 November 2012


Wider Environment

Newly Planted/Nurseries



Wider Environment



Ash Dieback Locations28 May 2013

Wider Environment




Wider Environment



Ash Dieback Locations16 June 2014

Wider Environment


Confirmed reports of Chalara ash dieback (Hymenoscyphus fraxineus) in the UK1 November 2012 to 6 October 2014

Data: Forestry Commission 2012-2014

Graphic: AshStat/Silviculture Research International 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

Cu

mu

lati

ve C

on

firm

ed

Re

po

rts

Days from Start of Outbreak

Nursery Sites Recently Planted Sites

Wider Environment Total

Ash Dieback Locations03 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.

LATEST SITUATION

Ash Dieback Locations03 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.

Proposed Map of Important Ash Locations

Source: Interim Chalara Control Plan, Defra 2012

Areas with widespread Chalarainfection 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.

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

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

Anatomy of an ash leaf

Compound leaf

Leaflet

Blade

Midrib

Rachis

Petiolule

Petiole

Photo: E. R. Wilson 2013

Model for the invasion and spread strategy of H. fraxineus in the woody sprout

1. Ascospore state2. 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

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

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

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

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 epicormicsprouting

– 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 2014Photo: Forest Research

http://www.forestry.gov.uk/chalara

Signs of disease

Source: Barnaby Wylder, Forestry Commission 2012 Source: Forest Research

Diamond-shaped lesions at branch unions Rapid dieback of branches and stems


Wilting leaves from early summer onwards Fruiting bodies on rachis of decaying leaves

Signs of disease

Trace Forward: Recently planted seedling showingsigns 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

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

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

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

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

Where there are high spore densities it is possible to see basal lesions associated with direct infection of the stem.

Lesions due to Hymenoscyphusfraxineus on the

stem of pole-stage ash

Photo: J. Clark 2014


Other things we need to be aware of with Ash treesAsh 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

There is often significant variation in flushing datesTwo veteran ash trees in Cumbria, 19 May 2014

(approximately 200 m apart)

Photos: E. R. Wilson 2014

Dasineura fraxinithe ash midrib gall midge Photo: E. R. Wilson 2013

Photograph courtesy of Nigel Straw, Forest ResearchThe ash bud moth Prays fraxinella,

is a native micromoth.Ash key gall caused by the

eriophyid mite Aceria fraxinivora.

Source: OPAL

Nectria canker is caused by the fungus Neonectria galligena.

Emerald Ash Borer (Agrilusplanipennis) is currently NOT

present in UK.

Source: OPAL

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

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

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

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

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

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

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

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

https://www.forestry.gov.uk/pestsanddiseases

https://www.forestry.gov.uk/treealert

livingashproject.org.ukProject partners:

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: [email protected]

First presented: 18 06 2014This version: v3.0, 08 06 2017