pests and pathogens - joan webber

Pest and Pathogens Problems Threatening

Britain’s Trees

Joan Webber, Principal Pathologist Forest Research

joan.webber@forestry.gsi.gov.uk

Birkbeck Institute of Environment, 4 November 2011

‘Established’ tree pests & diseases

Heterobasidion

root & butt rot

Honey fungus -

Armillaria

Hylobius

Changes in tree health? • Evidence base

• long term monitoring by active surveys

• expensive, therefore tend to be abandoned

• tend to focus on commercial species or single species in response to a particular pest or pathogen

• Passive surveillance

• FR Pest & Disease Diagnostic Advisory Service databases

• self reporting

• General perception that we are seeing increasing disease impacts on our trees

• changes in forestry practice, disturbance

• due to the introduction of new pests/pathogens

• Increase and diversity in free trade had never been greater and is now considered a major driver of pest introductions

• Growing affluence and disposable income means that consumers demand selection of food and plants from all over the world, and markets continually look for new products and more cost-effective production

• For Britain alone, many of 13,000 host/species/origin import combinations have been identified as potential risks

• Rule of 10 - only 10% of all introduced species will establish, and of these 10% will become pests, even fewer highly damaging pests

More introduced pests/pathogens?

x

Early examples of damaging introductions (GB)

Disease/Pathogen Pathways Possible Origin

Cinnamomi root disease

Phytophthora cinnamomi

Planting stock

1800s to 1900s

South west Pacific

White pine blister rust

Cronartium ribicola

Planting stock

1900s

Eastern Asia

Oak mildew

Erisiphe alphitoides

?

1900s

North America

Dutch elm disease

Ophiostoma ulmi

Elm logs

1920s

Eastern Asia

Fire blight

Erwinia amylovora

Planting stock &

infected fruit,1950s

USA

Red Band Needle Blight

Dothistroma septosporum

Planting stock

1950s

Himalayas, South

America?

UK major plant and tree pest introductions 1900-2010 (cumulative)

More recent damaging introductions

Disease/Pathogen Pathways Possible Origin

Dutch elm disease

Ophiostoma novo-ulmi

Elm logs 1960s Eastern Asia

Alder disease Phytophthora

alni

Nursery stock 1970s to

1990s

Interspecific

hybridisation event

Holly blight

Phytophthora ilicis

Nursery stock 1980s Unknown, Asia?

Sudden oak death

Phytophthora ramorum

Nursery stock 1990s Eastern Asia?

Horse chestnut bleeding

canker

Nursery stock 1990s Himalayas

Kernoviae dieback

Phytophthora kernoviae

Nursery stock 1990s New Zealand?

Lateralis root rot

Phytophthora lateralis

Nursery stock 2000s Europe, USA, Taiwan?

High risk pathways - plants • Regulation and inspection

• list based

• pathogens are microbes,

• symptoms non-specific

• The size issue! – instant trees

• commodities/products may not be homogeneous

• inspection difficult

• Cryptic pathogens and asymptomatic sporulation • Phytophthora ramorum

• Non-host carriers

Invasive species

• ‘Alien invasive species’ • as defined in the Convention on Biological

Diversity

• pose economic threat

• pose environmental threat, and impact on biodiversity

• Typically characterised as highly mobile, evolving entities

• Cause long term damage to the environment which may be irreversible

Changes that promote invasive behaviour

• Escape from ‘native’ habitat and stabilising selection

• Exposure to hosts that have not co-evolved resistance to the pathogen

• Mobility (association with a new/effective vector, this often includes man)

• Habitat disturbance and genetic change in the pathogen such as hybridisation

• Climate change

x

A newly arrived organism …

Fitness parameters Selection components

? Ge

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ottle

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Mu

tatio

n

2ry

intro

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ns

Se

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Intro

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n

Hyb

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After Brasier, 1987

Current disease problems in Britain

Red band needle blight

Corsican and lodgepole pine very susceptible

Horse chestnut bleeding canker

various Aesculus species affected

Acute oak decline (AOD)

a single agent disorder?

Phytophthora ramorum – ‘Sudden oak death’ (and P. kernoviae)

Pr an issue for ornamental plants (and gardens), but also beech, non-native oaks and now plantation larch

Other Phytophthora pathogens alder, sweet chestnut, Nothofagus, Lawsons cypress

Current pest problems in Britain

Dendroctonus – great spruce bark beetle present in continental Europe

Horse chestnut leaf miner particularly damaging on white horse chestnut

Oak processionary moth major defoliator of oak in Europe

Pine tree lappet moth widely distributed in Europe, extending into

Asia

Oak decline

Traditionally, oak decline considered a

syndrome, involving complex interactions

between several biotic and abiotic factors -

hosts, pests, pathogens, climatic/environment

factors

Increase in reports of oak dieback from 2002

2006 & 2007, first reports from Charnwood Forest, Leicestershire

Hatchlands (NT), Guildford, many trees affected in 2007

Charnwood reported rapid tree mortality: 2 trees in 2004, many by 2007/8

Charnwood first study site in 2009

Reports of oak mortality in Spain with similar symptoms

Chronology of events

Acute Oak Decline (AOD) Acute Oak Decline is the term given to oak trees

that develop symptoms over a short time and

high levels of mortality occur

In Britain we know of two types of AOD:

Foliage

Stem

Foliage type: Key agents are defoliating insects

and powdery mildew

Stem type: (Probably) bacteria and other agents

yet to be elucidated especially insect interaction

What is it?

Symptoms

Symptoms

Type of AOD

Currently a new episode of oak decline is taking place in Britain - Acute Oak Decline

Affected trees are identified by symptoms of extensive stem bleeding, and rapid decline and death (3-5 years)

At this stage organisms causing the ‘stem type’ of AOD probably include bacteria - new genus and species

Role that other factors play being elucidated – more information required (Agrilus beetles, other insects, root health, drought)

AOD – how long?

Searched the literature - Spanish connection

Suspect AOD has been ongoing Britain since mid 1990s

Revisited and re-interpreted advisory records

AOD – where?

Role of insect pests and Agrilus

Because evidence of a key role for bacteria

is growing, now unravelling how the

decline works (epidemiology)

Insects are likely to play a role in tree

mortality, possibly also transmission of the

bacteria

One insect commonly associated with

symptomatic trees is Agrilus biguttatus

Photos by Gyorgy Csoka, Hungary Forest Research Institute; Louis-

Michel Nageleisen,Département de la Santé des Forêts - France.

Results so far show there is a

significant co-occurrence of

AOD symptoms with exit

holes of Agrilus biguttatus

• In 2006, oak processionary moth, Thaumetopoea processionea was found at several London locations

• It is a major defoliator of oak in Europe.

• The caterpillars feed on the foliage of many species of oaks, including English, sessile and Turkey oak

• Apparently introduced on trees brought in for street landscaping scheme.

• London centred, but last year spread into Richmond Park

• Under active control

Oak Processionary Moth

21/11/2011 24

Ssssssspp

sssssss

Kitzingen, Germany June 2010

21/11/2011 25 sssssss

OPM caterpillars carry thousands of tiny irritating hairs that are dislodged on contact. They pose a considerable hazard to public health

0.1 mm

21/11/2011 26 sssssss

Breeding populations of OPM were first found in London in 2006

The moth was introduced as eggs on these 4-8m tall oak trees imported from the Netherlands

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The number of OPM larval nests located and destroyed each year:

2006 2007 2008 2009 2010

Richmond >100 171 424 2508 1910

Hounslow 0 458 53 361 424

Ealing 7 3 13 214 220

Brent 8 76 18 15 11

Hammersmith 0 0 0 2 0

Total: >115 708 508 3100 2565

** 44 OPM nests also found at Pangbourne, Berkshire, in August 2010 (arising from a separate introduction).

Oak Processionary Moth Outbreaks

with buffer zones, Dec 2010

21/11/2011 29

Pppppp

ppp

Pppppp

ppp

Controlling OPM is difficult and costly

• don’t bring large plants into the country

• unknown, non-listed pests are able to pass through our surveillance & monitoring systems

• eradication depends on an immediate & effective response

• control has been limited by:

- the available technology

- a lack of understanding of pest biology and ecology

- the difficulty of co-ordinating surveys & control

operations in an urban environment

• time & money

Lessons learnt?

Red band needle blight

June - JULY - August October May

Cause: Dothistroma septosporum - Dothistroma

needle blight

• There is a linear relationship

between volume loss and the

amount of defoliation

• Very evident in Corsican pine

• Affected trees show significant

reductions in:

• height

• diameter

• volume increment

• healthy and infected trees

• Also significant levels of tree death

in heavily affected areas

The impact

1999-2002 19 outbreaks

1955-1966 4 outbreaks

• 3 in nursery stock, Dorset

• 1 in south Wales

1989 1 outbreak in south Wales

7 out of 25 forest blocks

affected in East Anglia FD

History in Britain

Initially confined to

cases on Corsican pine

SP

LP

• By 2006, 70% of CP stands under

the age of 30 years infected

covering an area of 6,245 ha

• Starting to impact on lodgepole,

850 ha affected by 2008

• RBNB also found to be present

on 6 other pine species including

100 stands of P. sylvestris

Where is it?

2007-9 survey CP

Corsican pine Lodgepole pine Scots pine

21/11/2011 36

Plant Trade

Climatic conditions

Increase in frequency of days where

temperature => 18-20˚C with 3d rain +

0

1

2

3

4

5

6

7

70s 80s 90s 00s (00-05)

Fre

qu

en

cy

Why now?

Species composition

Large areas of single species

Reliance on a low number of

species

Increased diversity in the

pathogen

Multiple introductions, and adaptation

Heavy thin ~ 700 st ha-1

Disease management

Four years after thinning…

Some difference in disease impact %:

No thin District Thin Heavy thin

60% 52% 45%

and in terms of mean % mortality per stand:

No thin District Thin Heavy thin

13% 5% 3%

Disease management

Heavy thin treatment ca. 350 stems/ha

• Disease has increased rapidly since the late 1990’s

and is now present and will remain throughout

much of GB

• The host, genetic diversity in the pathogen and

changing climate have all favoured the disease

• Significant volume loss and mortality are occurring,

impacting on future timber revenues

• Future management will involve changes to

species choice and silvicultural practice

• This raises policy issues surrounding forest

sustainability, global plant trade and climate

change

Lessons learned?

21/11/2011 40 sssssss

• a major pest of Scots pine in C & E

(not native to the British Isles).

• can cause severe / total defoliation

and tree death.

• capable of major outbreaks, e.g.

83,700 ha damaged in NE Germany

in 1993-96.

• new outbreaks in Germany and

Poland in 2009 & 2010.

• breeding population discovered in

pine plantations near Inverness in 2008/2009

• under active controls

Pine-tree Lappet Moth (Dendrolimus pini)

Pine-tree Lappet Moth

Horse chestnut leaf miner

damage: first seen in Britain

in 2002

Horse chestnut leaf miner

21/11/2011 42 bbbbbb

Distribution in 2010:

Horse chestnut leaf miner, Cameraria ohridella

Horse chestnut bleeding canker

Non-specific symptom,

caused by various known

fungal pathogens

Where is it?

2002 2003 2004

2005 2006 2007

Isolating from necrotic bark found a species of gram-negative fluorescent bacterium that turned up consistently

Corresponded to Pseudomonas syringae, which is a species with many pathovars that attack a huge range of plant species (bean/pea/tomato/cherry/elm)

A new pathogen?

+ive -ive

What is it?

New cause of horse chestnut bleeding canker

Previously Pae only found associated with Aesculus indica in India in 1970’s, causing a leaf disease – an introduction?

Affected trees often have multiple cankers, so branches and stems may be girdled

Disease is very obvious on young trees (thin bark, quickly girdled)

Summary

Pae has been the subject of collaborative project on genome sequencing, which has provided insights into the pathogen

British strains of Pae probably originate from a single, recent introduction into Britain, and may have descended from an Indian strain

It has acquired a suite of ‘unique’ genes and genetic pathways which may enable it to infect and live in the woody parts of horse chestnuts

Work underway studying ability to survive spread in soil and water

Phytophthora diseases

Phytophthora - genus of aggressive plant pathogens (most famous potato blight)

Known as ‘water moulds’, because they have swimming spores, which are released and swim actively in water. Need water to infect

Currently have several Phytophthora diseases that are highly damaging to trees in Britain; some of them recognised quarantine pathogens, others around for longer, but with recently increased impact

Phytophthora tree diseases

Characteristic of some Phytophthoras that they can have very wide host range – ie attack many, many species of plants eg P. cinnamomi, probably fewer specialist species, eg P. ilicis

Most introduced species - probably arriving via plant trade and plant collectors

Then exposed to guilds of plants without co-evolved resistance

Recent rash of new Phytophthora arrivals

Phytophthora ilicis attacking

holly leaves: symptoms Feb-

March

Old Phytophthora problem - Castanea

Ink disease of sweet chestnut - south of England

Dieback of maidens and coppice

P. cinnamomi attacks the roots & root collar

First recorded in New Forest in 1930s

Now apparently much more prevalent

Poor coppice regeneration

Current activity

of P. cinnamomi

Activity with 1.5oC

temperature

increase

Activity with 3oC

temperature

increase

P. cinnamomi distribution scenarios

Threat related to climate change

Most recent Phytophthora problems in Britain

Several characterised as aerial Phytophthoras

may not infect roots at all

attack above ground parts of trees causing aerial lesions (on leaves, shoots, trunks and branches)

Dieback of Nothofagus (Phytophthora pseudosyringae)

Holly blight (Phytophthora illicis)

Ramorum disease of larch (Phytophthora ramorum sudden oak death in the USA)

1994

2000

2006

1996

2002

1998

2004

2008

2009

Emergency legislation implemented (P. kernoviae)

Emergency legislation implemented (P. ramorum)

First symptoms (USA)

First symptoms (Europe)

Phytophthora sp. identified (Europe)

Phytophthora sp. identified (USA)

Link between USA / Europe disease

First UK finding (ornamental)

Phytophthora kernoviae identified

P. ramorum described PHSI surveys begin

First UK finding (tree)

First UK finding on Heathland

European Pest risk analysis

First finding on commercial tree crop (Jap larch)

2010

Timeline

RAPRA project starts

1 EU, 2 NA lineages

Bleeding lesions on beech

Inoculum from

rhododendrons

Phytophthora ramorum

Emerging findings: Aug-Sept 2009

JL foliar symptoms, Aug-Sept 2009

Findings over the past year

2009 larch dieback and mortality widespread in forests across the west country; first findings in Wales in May 2010, Northern Ireland in July Symptoms on affected larch - needle loss, dieback of

fine branches leading to cankers on main branches and trunk

Mature trees (25-40 years) have multiple cankers, eg 35cm dbh tree, with more than 80 individual resinous cankers

So far, infection mainly on Japanese larch, but also confirmed on European and hybrid larch

Many other trees species affected when in close proximity to infected larch. Spores come from larch

Changes in Britain

21/11/2011 58

Lab infected JL needles

Naturally infected JL needles

Infection on 5-7 y Douglas fir

Canker

on

stem

Mature J L

DF

Mature J L

21/11/2011 61

Surveillance

Total Pr Sites + Climate Prediction

Current future management Spread distances via ‘natural’ movement Timing of sporulation and expression of

symptoms Sporulation potential on hybrid and European

larch Bark susceptibility of larch species

Future predictions about disease Emergence of possible new genotypes and

lineages introduction New era of Phytophthoras on conifers (Pr, P.

lateralis, P. pinifolia – one waiting in the wings) Aerial Phytophthoras more likely with climate

change?

Key questions

Challenges ahead!

Successes in pest and disease control

Control of great spruce bark beetle with R. grandis

Management of root and but rot with PG Suspension and urea

Resistant elms

Management practices

Invasive pests and pathogens need ongoing management, for the old and the new

Vigilance and your help to counter new introductions

Better awareness about changes in the health of our trees

Conclusions

Forest Research, Centre for Forestry & Climate Change Anna Brown (Dothistoma needle blight): Alice Holt

Sandra Denman (AOD): Alice Holt

Nigel Straw (OPM, horse chestnut leaf miner): Alice Holt

Sarah Green (horse chestnut bleeding canker); NRS

Roger Moore (Pine-tree Lappet Moth): NRS

Pest & Disease Diagnostic Advisory Service

Christine Tilbury, David Rose, Steven Hendry

ddas.ah@forestry.gsi.gov

ddas.nrs@forestry.gsi.gov

Acknowledgements