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Pest and Pathogens Problems Threatening
Britain’s Trees
Joan Webber, Principal Pathologist Forest Research
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
ne
tic b
ottle
ne
ck
Mu
tatio
n
2ry
intro
du
ctio
ns
Se
x
Intro
gre
ssio
n
Hyb
ridis
atio
n
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
21/11/2011 27 sssssss
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
Acknowledgements