Update on Pests and Diseases of Trees Joan Webber, Principal Pathologist Tree Health Forestry & Climate Change Centre AA Annual Conference, Reading 4 th 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 sycamoreOak mildewScab on SorbusVerticillium 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 Quercus species affectedInfested trees% of total Q. cerris14411 Q. robur v. fastigiata20.2 Q. frainetto10.1 Q. x hispanica10.1 Q. x robur60.5 Q. ilex90.7 Q. petraea40.3 Q. robur Q. turnerii10.1 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– 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 km 2

Pppppp ppp Pppppp ppp Controlling OPM is difficult and costly

Increase in reports of oak dieback from & 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 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

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 willow More 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   Acknowledgements