Update on Pests and Diseases of Trees

Joan Webber, Principal PathologistTree Health Forestry & Climate Change Centre

AA Annual Conference, Reading 4th September 2012

Defra-FC Tree Health Action Plan

Arrival of damaging pests and pathogens in Britain

• Cold February with frosts and snowfall• Third warmest March since records

began • Wettest April for over 100 years• Twice the usual amount of rain in June• Summer fourth wettest since records

began in 1727• September warmer than average?

Weather impacts – pests and diseases

Impact of weather

Cristulariella on sycamore Oak mildew Scab on Sorbus Verticillium wilt

Anthracnose, plane

Prolonged surface wetness on leaves

Flooding or water-logging of soil

Alternating rain and sun

Recent tree disorders Oak processionary moth

Thaumetopoea processionea Acute oak decline (AOD)

Single agent disorder? Phytophthora lateralis

Lawson cypress, outbreaks apparently geographically scattered

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

• It is a major defoliator of oak in Europe

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

• Arrived on 4-8 m tall imported oak for street landscape plantings

Oak Processionary Moth

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

0.1 mm

Ssssssspp

sssssss

Kitzingen, Germany June 2010

Affected Quercus species

Nests 2007

Nests 2008

Nests 2009

Nests 2010*

Nests 2011

708 508 2450 2176 4410

Quercus species affected Infested trees % of total

Q. cerris 144 11

Q. robur v. fastigiata 2 0.2

Q. frainetto 1 0.1

Q. x hispanica 1 0.1

Q. x robur 6 0.5

Q. ilex 9 0.7

Q. petraea 4 0.3

Q. robur 1141 87.2

Q. turnerii 1 0.1

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

Hhhh

sssssss

OPM outbreak area in London, 2006–2011

2011

2008

5 km

2010

• on average, the population has spread at a rate of 0.9 km per year

• the outbreak in London now covers an area of 99 km2

Pppppp

ppp

Pppppp

ppp

Controlling OPM is difficult and costly

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

Reports of oak mortality in Spain with similar symptoms

Acute Oak Decline (AOD)

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 catagorise two types of AOD: Foliage Stem

Foliage type: Key agents are defoliating insects and powdery mildew

Stem type: (Probably) bacteria and other agents including insects

What is it?

Symptoms

Type of AOD

A new episode of acute oak decline is taking place in Britain – stem attacking

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

Sometimes trees also recover

At this stage organisms causing the ‘stem type’ of AOD probably include bacteria – newly described genera and species, as well as other insects, root health, drought

Distribution – mainly midlands and south east

Reports of AOD – 2006 and 2012

2006 2011

Symptoms and players

Agrilus biguttatus

Bacterial lesions

Role of insect pests and Agrilus Evidence of a key role for bacteria is

growing, and now unravelling how the decline works

Insects are likely to play a role in tree mortality, possibly also transmission of the bacteria

The 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.

Our results so far show there is a significant co-occurrence of AOD symptoms with exit holes of Agrilus biguttatus

Why now!

D-shaped holes

• Phytophthora lateralis• Infects Lawson cypress• Previously known in the USA,

origins in Taiwan• Recent outbreaks in France &

Netherlands• Found in Scotland in November

2010• Now 6+ outbreak areas known

(mainly 30 mile radius Glasgow)• Mature trees killed• Two infected sites in England

(2011) and one in Wales (2012)• England outbreaks: one in

Devon, other in Yorkshire

Another Phytophthora on the block

New outbreak in Wales

Photo: C. Robin INRA, Bordeaux

• Since 2008 FR part of a collaboration to find origin of Phytophthoras such as P. ramorum

• Discovered P. lateralis in Taiwan in 2008, foliar pathogen in 2010

• Origin probably Taiwan/ Japan• With IT/US/Tai/F partners looking

at genetic differences between US- Taiwanese-European populations

• Potential for hybridisation with P. ramorum

• Pathogenicity, some host testing to determine any wider risk

More recent arrivals Chestnut blight

Cryphonectria parasitica Ash dieback

Chalara fraxinea (= Hymenoscyphus pseudoalbidus)

Asian Longhorn Beetle (ALB) Anaplophora glabripennis

Chestnut blight Causal agent – fungus

Cryphonectria parasitica Quarantine pathogen that has

long been regarded as high risk

Now known to be native to eastern Asia, it was accidentally introduced into the USA more than a 100 years ago and caused the demise of the American chestnut (4 billion trees)

It can also infect and sporulate on some species of oak in the USA

First seen in Italy in 1938 Only countries free of disease

NL, EI and UK

Spread of chestnut blight in Europe

Robin and Heiniger (2001)

Symptoms

Images courtesy D. Rigling

Potential for spread of chestnut blight in GB? Cryphonectria parasitica – good

controls in place to prevent spread in wood (debarking/ inspection)

But… Spread of disease almost

throughout all EU MS Demand for plants for nut

production, more imports Lack of awareness about the risks Apparently a long latent period

before infection shows up Three outbreaks in recent

plantings (5 or less years) Centralised distribution Evidence suggests not

widespread

Prognosis? Not all doom and gloom! In Europe the disease is largely

managed through a natural biological control

Hypovirulence Virus which debilitates the

pathogen C. parasitica Spreads from hypovirulent (virus

infected genotypes, to virulent genotypes, converting them to less pathogenic forms

Providing there is not too much variation in the C. parasitica population, these viruses will spread and take effect

With hypovirulence, cankers go into remission and ‘heal’, dieback is arrested

Spread of Chalara fraxinea in Europe

Kiristits (2011)

Symptoms of ash dieback first documented in eastern Europe in 1990s

In 2006, first formal publication that a new pathogen was involved

Origins unknown

Chalara fraxinea symptoms

Dieback so severe in some countries, 60-90% of trees are affected in some locations

eg Poland, Denmark, Lithuania

Chalara fraxinea symptoms• Not to be confused with the ash

dieback that was first characterised in Britain in the 1980s (Pawsey; Hull & Gibbs)

• Confusingly, also known as Hymenoscyphus pseudoalbidus

• Currently only found in nurseries or recently planted areas

• One recent outplanting in Scotland (3-4 years); one in England (2011/12 winter)

• Fraxinus excelsior apparently highly susceptible, F. nigra and F. angustifolia slightly less so, F. americana much less

• Sporulates on fallen leaves

Currently many questions

Spread beyond recent plantings in the UK? Host range? Is it only the genus Fraxinus? Where has its come from? Its closest relative is a

considered a native (both in GB and wider Europe) and is a non-damaging agent coloniser of fallen ash leaves

Natural spread - how far, how fast? Resistant genotypes in the ash population?

Assessment of the risk posed by this pathogen has been undertaken by Forest Research pathologists and is now available for consultation via Fera website – have your say

Asian Longhorn Beetle• Affects a wide range of broadleaf tree

species• Typically arrives in untreated packaging• Now epidemic in parts of USA, causing

damage valued at $3.5 billion each year• With its ‘cousin’ CLB, starting to have an

impact in some European countries

Asian Longhorn Beetle Outbreak in Kent – March 2012

ALB eradication: March – August

Most frequently affected trees: sycamore, poplar and willowMore than 100 trees infested, and many larvae and pupae

Challenges ahead! Control and eradication can also be difficult

and expensive Invasive pests and pathogens need ongoing

management, but don’t ignore the old foes Dutch elm disease, horse chestnut bleeding

canker and leaf miner are still there and still important

Vigilance and your help to counter new introductions

Better awareness about changes in the health of our trees

End note

Forest Research, Centre for Forestry & Climate Change

Sandra Denman (oak decline): Alice Holt Nigel Straw, Dave Williams (OPM, ALB, horse

chestnut leaf miner, ALB): Alice Holt Joan Webber, Steven Hendry, Gavin Hunter (ash

dieback and chestnut blight); Alice Holt and NRS Sarah Green (Phytophthora lateralis); NRS Pest & Disease Diagnostic Advisory Service

Christine Tilbury, David Rose, Steven Hendry ddas.ah@forestry.gsi.gov ddas.nrs@forestry.gsi.gov

Acknowledgements