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Principal Pathologist and project leader

Responsible for advising on pathogens impacts and undertaking research into the health of trees, with particular emphasis on recently arrived pests and pathogens.

Joan Webber graduated from the University of Wales, Aberystwyth, with a BSc in Botany and Microbiology in 1975. She studied for her PhD in tree pathology as a SRC CASE student with the University of Wales and the Forestry Commission from 1975-78.

From 1979 Joan then worked as a research fellow and lecturer employed by the University of Southampton where her research focussed on Dutch elm disease and the interplay between the tree pathogens and insect vectors.

She joined Forest Research in 1989, initially as Head of Forest Products research and then transferred to Pathology in 1996, becoming Principal Pathologist in 2001.

  • Detection, diagnosis and epidemiology of recently arrived pathogens including P. ramorumP. lateralis and Hymenoscyphus fraxineus (ash dieback)
  • Variation and genotyping of tree pathogens
  • Origins of introduced invasive Phytophthora pathogens
  • Pest risk analysis
  • Disease management and extension.

Much of this research is undertaken in collaboration with scientists at UK based and international organisations including Fera, Imperial College, AFBI, University of Tuscia, University of Sassari, USDA Forest Service, University of California Davis, Taiwan Forestry Institute, Scion New Zealand and FABI (South Africa).


  • Member of the British Mycological
  • Member of IUFRO Unit 7.02.09 ‘Phytophthoras in Forests and Natural Ecosystems’
  • Member of the International Forestry Quarantine Research Group
  • EPPO Forestry panel member
  • Member of the Forestry Commission GB and Northern Ireland Tree Health Advisory Group
  • Core member of Defra Plant Health Risk Management Group
  • Participant in Horizon 2020 POnTE project (Pest Organisms Threatening Europe)
  • Recipient of the Institute of Chartered Foresters’ medal to mark professional excellence in forest pathology (2014)
  • Peter Savill Award in recognition of a significant contribution to the British Forest Industry (2016)
Principal Pathologist
Tree health

Alice Holt

Alice Holt Lodge




Related Research


Ecology and Pathology of Ash Dieback Disease

This project investigated the factors that influence infection by the ash dieback pathogen (Hymenoscyphus fraxineus) and the long-term outcomes for affected ash trees.

Status completed


Mapping the Distribution of Phytophthoras in Britain

This project is mapping the distribution of Phytophthora species across Britain to understand the extent of the risk they pose to tree hosts.

Status current
Focus on emerging Phytophthoras

Emerging diseases of forests caused by new and exotic Phytophthora species (POnTE project)

Genetic variation in the ash dieback pathogen

Project about the biology of Chalara ash dieback pathogen at Forest Research

Ecological genetics of the ash dieback pathogen

The research will investigate the ecological genetics of the ash dieback pathogen Hymenoscyphus pseudoalbidus and its ability to evolve in response to natural selection.

Chalara research

Information about research carried out by Forest Research on Chalara ash dieback.

Clearance and disposal strategies for Phytophthora-infected rhododendron

Project to identify new or improved management strategies for the eradication and safe disposal of Phytophthora-infected rhododendron, and methods which reduce pathogen persistence on infected sites

Phytophthora kernoviae

Overview of invasive plant pathogen Phytophthora kernoviae. Distribution, symptoms, diagnosis and management.

Impact of Phytophthora diseases on trees

Research programme focussed on assessing the impact of Phytophthora ramorum and Phytophthora kernoviae

Related Publications


[Archive] Dutch elm disease in Great Britain

RIN 252 (1994) Out of print research publications from the 1980s and 1990s. Please note that since publication the products named may have been withdrawn or changed formulation, services may no longer be available, legislation superseded and addresses and contacts changed.



Hot-water treatment as a possible method for eradicating Chalara fraxinea (Hymenoscyphus pseudoalbidus) infection from ash fruits (Fraxinus excelsior L)

Treating ash seeds with hot water may kill Chalara infection Immersing ash seeds in 44 °C water for 5 hours may eradicate Chalara infection in ash seeds without significantly reducing the viability of the seeds. Forest Research scientists have published the results of this trial in Quarterly Journal of Forestry. Batches of ash fruits were subjected […]

Impacts of climate change on forests in Scotland

Report compiled for Forestry Commission Scotland by Duncan Ray with sections also drafted by Dave Wainhouse, Joan Webber and Barry Gardiner.

[Archive] Water storage of timber: experience in Britain

From time to time a calamity such as forest fire or violent storm requires that timber is salvaged quickly. Where such timber is plantation grown the investment loss that major destruction brings is catastrophic unless the most valuable timber can be saved and then marketed in an orderly way. This Bulletin reports on a successful […]

Other Research

‘Understanding Biotic Threats’ and ‘Delivering Resilient Forests’

Programme Work Package Manager for Forestry Commission funded research which underpins advice on tree health issues, and includes national and international collaborative research with universities and other research agencies and institutes. The overarching aim is to improve our understanding and management of the pests and pathogens which affect trees.

Peer reviewed journal articles

Peer reviewed journal papers and book chapters

Brasier CM, Webber JF (2019). Is there evidence for post-epidemic attenuation in the Dutch elm disease pathogen Ophiostoma novo-ulmi? Plant Pathology https://doi:10.1111/ppa.13022

Kalantarzadeh M, Mulholland DA, De Leij FAAM, Webber JF. (2019). Induced antimicrobial activity in heat-treated woodchips inhibits the activity of the invasive plant pathogen Phytophthora ramorum. Plant Pathology https://doi:10.1111/ppa.13010

Perez-Sierra A,  Romon-Ochoa P, Gorton C, Lewis A, Rees H, Van Der Linde S,  Webber J (2019). High vegetative compatibility diversity of Cryphonectria parasitica infecting sweet chestnut (Castanea sativa) in Britain indicates multiple pathogen introductions. Plant Pathology https://doi:10.1111/ppa.12981

Orton ES, Clarke M, Brasier CM, Webber JF, Brown JKM. (2018) A versatile method for assessing pathogenicity of Hymenoscyphus fraxineus to ash foliage. Forest Pathology

Webber JF Brasier CM, 2018. Ramorum Disease of Larch. In: Hansen EM, Lewis KJ, Chastagner GA 614 (eds) Compendium of Conifer Diseases (second edition). St. Paul, MN, USA: APS Press.

Harris AR, Mullett M, Webber JF. (2018). Changes in the population structure and sporulation ability of Phytophthora ramorum associated with the epidemic on Larix (larch) in Britain. Biological Invasions 20 (9), 2313-2328.

Wylder B, Biddle M, King K, Baden R, Webber J (2018). Mortality dating of Fraxinus excelsior to assess the arrival of ash dieback (Hymenoscyphus fraxineus) in England. Forestry 91 (4), 434–443 http://doi:10.1093/forestry/cpx059

Perez-Sierra A, Webber J, Birchall E, Carson-Taylor L. (2017). Things you need to know about Xylella fastidiosa. Forestry & Timber News December 2017, 42-44.

Orton ES, Brasier CM, Bilham L, Bansal A, Webber JF, Brown JKM. (2017). Local population structure of the ash dieback pathogen, Hymenoscyphus fraxineus, in relation to its mode of arrival in the UK. Plant Pathology, DOI: 10.1111/ppa.12762.

Brasier C, King K, Kirisits T, Orton E, Webber J (2017). High frequency of vegetative incompatibility combined with haploid selfing in the native European ash foliage coloniser Hymenoscyphus albidus. Fungal Ecology 28

Lewis A, Gorton C, Rees H, Webber J, Pérez-Sierra A. (2017). First report of Gnomoniopsis smithogilvyi causing lesions and cankers of sweet chestnut in the United Kingdom. New Disease Reports 35, 20.

Clark J, Webber J. (2017). The ash resource and the response to ash dieback in Britain. In: Dieback of European Ash (Fraxinus spp.): Consequences and Guidelines for Sustainable Management; Editors: R. Vasaitis & R. Enderle, pp.228-237. Swedish University of Agricultural Sciences, Uppsala.

Vettraino AM, Brasier CM, Webber JF, Hansen EM, Green S, Robin C, Tomassini A, Bruni N, Vannini A. (2017). Contrasting microsatellite diversity in the evolutionary lineages of Phytophthora lateralis. Fungal Biology 121 (2), 112-126.

Wainhouse D, Inward DJG, Denman S, Green S and Webber JF (2016). Climate Change: 7 Insect pests and pathogens. LWEC Agriculture and Forestry Climate Change Report Card Technical Paper

King KM, Webber, JF. (2016). Development of a multiplex PCR assay to discriminate native Hymenoscyphus albidus and introduced H. fraxineus in Britain and assess their distribution. Fungal Ecology 23, 79-85.

Kasuga T, Bui M, Bernhardt E, Swiecki T, Aram K, Cano LM, Webber, J, Brasier C, Press C, Grünwald NJ, Rizzo DM, Garbelotto M. (2016). Host-induced aneuploidy and phenotypic diversification in the Sudden Oak Death pathogen Phytophthora ramorum. BMC Genomics 17, 385-101. DOI: 10.1186/s12864-016-2717-z

Harris AR, Webber JF. (2016). Sporulation potential, symptom expression and detection of Phytophthora ramorum on larch needles and other foliar hosts. Plant Pathology 65 (9), 1441-1551. DOI: 10.1111/ppa.12538

Mullett M, Tubby K, Webber J, Brown A. (2016). A reconsideration of natural dispersal distances of the pine pathogen Dothistroma septosporum. Plant Pathology 65 (9), 1462-1472. DOI: 10.1111/ppa.12522

Kerr G., Webber, J., Mason, W., Jinks, R. and Jennings, T. (2015). Building resilience into planted forests: recent experience from Britain. XIV World Forestry 7-11 September 2015, Congress, Durban, South Africa.

Freer-Smith PH, Webber, JF. (2015). Tree pests and diseases: the threat to biodiversity and the delivery of ecosystem services. Biodiversity and Conservation DOI: 10.1007/s10531-015-1019-0

Scanu B, Webber JF. (2015), Dieback and mortality of Nothofagus in Britain: ecology, pathogenicity and sporulation potential of the causal agent Phytophthora pseudosyringae. Plant Pathology. 65, 26–36. DOI: 10.1111/ppa.12399

King KM, Harris AR, Webber JF, 2015. In planta detection used to define the distribution of the European lineages of Phytophthora ramorum on larch (Larix) in the UKPlant Pathology 64, 1168-1175. DOI: 10.1111/ppa.12345.

McCartan SA, Webber JF, Jinks RL. (2015) Hot-water treatment as a possible method for eradicating Chalara fraxinea (Hymenoscyphus pseudoalbidus) infection from ash fruits (Fraxinus excelsior L). Quarterly Journal of Forestry 109, 18-23.

Denman S, Brown N, Kirk S, Jager M, Webber J. (2014). A description of the symptoms of Acute Oak Decline in Britain and a comparative review on causes of similar disorders on oak in Europe. Forestry 88 (1), 53-63 DOI: 10.1093/forestry/cpu010

Brasier CM, Webber JF. (2013). Vegetative incompatibility in the ash dieback pathogen Hymenoscyphus pseudoalbidus and its ecological implications. Fungal Ecology 6(6), 501-512.

Franceschini S, Webber JF, Sancisi-Frey S, Brasier CM. (2013). Gene×environment tests discriminate the new EU2 evolutionary lineage of Phytophthora ramorum and indicate that it is adaptively different. Forest Pathology DOI: 10.1111/efp.12085

Mullett MS and Webber JF (2013) Pseudomonas syringae pv. aesculi: foliar infection of Aesculus species and temperature–growth relationships. Forest Pathology 43 (2013) 371–378 DOI: 10.1111/efp.12040

Hunter, G.C., Wylder, B., Jones, B. and Webber, J.F. (2013). First finding of Cryphonectria parasitica causing chestnut blight on Castanea sativa trees in England. New Disease Reports 27,1. DOI: 10.5197/j.2044-0588.2013.027.001

Brasier CM, Franceschini S, Vettraino AM, Hansen EM, Green S, Robin C, Webber JF, Vannini A. (2012). Four phenotypically and phylogenetically distinct lineages in Phytophthora lateralis. Fungal Biology 116, 1232-1249.
Green S, Webber JF. (2012). The emerging threat from Phytophthora to trees in Scotland. Scottish Forestry 66, 9-16.

Green S, Brasier CM, Schlenzig A, McCracken AR, Wilson M, MacAskill GA, Webber, J.F. (2012). The destructive invasive pathogen Phytophthora lateralis found on Chamaecyparis lawsoniana across the UK. Forest Pathology 43, 19-28.

Van Poucke K, Franceschini S, Webber JF, Vercauteren A, Turner JA, McCracken A, Heungens K., Brasier CM. (2012). Discovery of a fourth evolutionary lineage of Phytophthora ramorum: EU2. Fungal Biology 116, 1178-1191.

Scanu, B., Jones, B. and Webber, J.F. (2012). A new disease of Nothofagus in Britain caused by Phytophthora pseudosyringae. New Disease Reports 25, 27.

Fichtner, E. J., Rizzo, D. M., Kirk, S. A. and Webber, J. F. (2011). Infectivity and sporulation potential of Phytophthora kernoviae to select North American native plants. Plant Pathology DOI: 10.1111/j.1365-3059.2011.02506.

Webber, J.F., Vettraino, A.M., Chang, T.T., Bellgard, S.E., Brasier, C.M. and Vannini, A. (2011). Isolation of Phytophthora lateralis from Chamaecyparis foliage in Taiwan. Forest Pathology DOI: 10.1111/j.1439-0329.2011.00729.x

Fichtner, E. J., Rizzo, D. M., Kirk, S. A. and Webber, J. F. (2011). Root Infections May Challenge Management of Invasive Phytophthora spp. in U.K. Woodlands. Plant Disease 95(1), 13-18.

Beale, E., Webber, J.F. and Eaton, R.A. (2010). Comparative susceptibility of pine, spruce and larch to sapstain. Forest Pathology 40(2), 116-128.

Tubby, K.V. and Webber, J.F. (2010). Pests and diseases threatening urban trees under a changing climate. Forestry 83, 451-459.

Brasier, C.M. and Webber, J.F. (2010). Sudden larch death. Nature 466(7308), 824-5.

Webber, J.F. (2010). Pest risk analysis and invasion pathways for plant pathogens. New Zealand Journal of Forestry Science 40, S45-56.

Denman, S., Kirk, S.A., Moralejo, E.and Webber J.F. (2009). Phytophthora ramorum and P. kernoviae on naturally infected asymptomatic foliage. EPPO Bulletin 39, 105-111.

Webber, J. (2009). Management of Phytophthora kernoviae and P. ramorum in southwest England. In: Frankel SJ, Kliejunas JT, Palmieri KM, eds. Proceedings of the Sudden Oak Death Third Science Symposium, pp. 177-183. General Technical Report PSW-GTR-214. Albany, CA, USA: Pacific Southwest Research Station, US Forest Service.

Denman, S. and Webber, J. (2009). Oak declines: new definitions and new episodes in Britain. Quarterly Journal of Forestry 103(4), 285-290.

Kozlakidis, Z., Hacker, C.V., Bradley, D., Jamal, A., Phoon, X., Webber, J., Brasier, C.M., Buck, K.W., and Coutts, R.H.A. (2009). Molecular characterisation of two novel double-stranded RNA elements from Phlebiopsis gigantea. Virus Genes 39(1), 132-6.

Broadmeadow, M.S., Webber, J.F., Ray, D. and Berry, P. (2009). An assessment of likely future impacts of climate change on UK forests. In: Combating climate change – a role for UK forests. An assessment of the potential of the UK’s trees and woodlands to mitigate and adapt to climate change, pp 67-99; (eds Read, D., Freer-Smith, P.H., Morison, J., Hanley, N., West, C., Snowdon, P. and Broadmeadow, M.). The Stationery Office, Edinburgh.

Webber, J.F., Parkinson, N.M., Rose, J., Stanford, H., Cook, R.T.A. and J.G. Elphinstone (2008). Isolation and identification of Pseudomonas syringae pv. aesculi causing bleeding canker of horse chestnut in the UK. Plant Pathology 57(2), 368.

Webber, J.F. and Rose J. (2008). Dissemination of aerial and root infecting Phytophthoras by human vectors. In: Proceedings of the Sudden Oak Death Third Science Symposium (eds Frankel, S.J., Kliejunas, J.T., & Palmieri, K.M.) pp. 195-198. Gen. Tech. Rep. PSW-GTR-214, Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. 491 p.

Tubby, K.V., Scott, D. and Webber, J.F. (2007). Relationship between stump treatment coverage using the biological control product PG Suspension and control of Heterobasidion annosum on Corsican pine (Pinus nigra subsp. laricio). Forest Pathology 38(1), 37-46.

Denman, S., Kirk, S.A., Brasier, C.M., Hughes, K.J.D., Barton, V.C., Griffin, R. and Webber, J.F. (2006). Phytophthora ramorum on Quercus ilex in the UK. Plant Disease 89, 1241.

Denman, S., Kirk, S.A., Whybrow, A., Orton, E. and Webber, J.F. (2006). Phytophthora kernoviae and P. ramorum: host susceptibility and sporulation potential on foliage of susceptible trees. EPPO Bulletin 36 (2), 373–376.

Brown, A., Brasier, C., Denman, S. Rose, J., Kirk, S., and Webber, J. (2006). Tree hosts as aerial Phytophthora infections with particular reference to P. ramorum and P. kernoviae at two UK survey sites. In: Progress in Research on Phytophthora Diseases of Forest Trees (Proceedings of the IUFRO conference on Phytophthora pathogens of trees, Freising, 11–17 September 2004), eds. C. Brasier, T. Jung and W. Oβwald, pp. 122-125.

Brown, A., Brasier, C. and Webber, J. (2006). Aetiology and distribution of Phytophthora kernoviae and P. ramorum stem lesions on European beech in southwest England. In: Progress in Research on Phytophthora Diseases of Forest Trees (Proceedings of the IUFRO conference on Phytophthora pathogens of trees, Freising, 11–17 September 2004), eds. C. Brasier, T. Jung and W. Oβwald, pp. 139-141.

Strong, N., Webber, J.F. and Eaton, R.A. (2005). Factors affecting the fungal colonisation of pine lumber. Forest Pathology 35, 195-203.

Webber, J.F. and Brasier, C.M. (2005). Global pathways for tree pathogens; the challenges of Phytophthora species as invasive threats. In: Proceedings of the BCPC International Congress – Crop Science & Technology 2005, volume 2, 741-748. BCPC, Omega Park, Alton, Hampshire.

Webber, J.F. and Brasier, C.M. (2005). Invasive pathogens – from Dutch elm disease to sudden oak death. In: BCPC Symposium Proceedings 81 (Introduction and Spread of Invasive Species), 35-40.

Thorpe, K. and Webber, J.F. (2005). Optimisation of a biological control agent for Heterobasidion annosum in the UK. In Proceedings of the 11th IURFO International Conference on Root and Butt Rots, Poznanń, Poland 16-22 August 2004 (eds. M. Mańka, P. Lakomy) pp.433-340. The August Cieszkowski Agricultural University: Poznań, Poland.

Deman, S., Kirk, S.A., Brasier, C.M. and Webber, J.F. (2005). In vitro Leaf Inoculation Studies as an Indication of Tree Foliage Susceptibility to Phytophthora ramorum in the UK. Plant Pathology 54, 512–521.

Denman, S., Kirk, S.A., Rose, J., Webber, J.F., and Brasier, C.M. (2004). Phytophthora ramorum wound inoculations of conifer saplings important to British forestry. In Proceedings of the 51st Western Forest Disease Work Conference: 18-22 August 2003, Grants Pass, OR, ed. B.W. Geils, pages 55-57. USDA Forest Service, Rocky Mountain Research Station: Flagstaff, AZ.

Brasier, C.M., Denman, S., Rose, J, Kirk, S.A., Lane, C., Hughes, K., Griffin, R., Inman, A. and Webber, J.F. (2004). First report of ramorum bleeding canker on Quercus falcata, caused by Phytophthora ramorum. Plant Pathology 53, 804.

Brasier, C., Denman, S., Brown, A. and Webber, J. (2004). Sudden oak death (Phytophthora ramorum) discovered on trees in Europe. Mycological Research 108, 1108-1110.

Gorton, C., Kim, S.H., Henricot, B., Webber, J. and Breuil, C. (2004). Phylogenetic analysis of the bluestain fungus Ophiostoma minus based on partial ITS rDNA and ß-tubulin gene sequences. Mycological Research 108, 759-765.

Popular articles and Forestry Commission information notes

Webber, J., Tilbury, C., Steele, H. and Rose, D. (2011). Potential impacts of pests and pathogens on short rotation forestry in Britain. In: Short Rotation Forestry: review of growth and environmental impacts (PDF-3255K). (McKay, H. ed.) Forest Research Monograph, 2, Forest Research, Surrey, 212pp.

Webber, J. (2011). Tree disease – why this wood is fighting for its life. Countryside Matters, July 2011 issue, 16-18.

Martin, S. and Webber, J. (2009). Phytophthora update. Forestry and Timber News October 2009, 26.

Brown, A. and Webber, J. (2008). Red Band Needle Blight of Conifers in Britain (PDF-1200K). Forestry Commission Research Note 2. Forestry Commission Edinburgh. 8pp

Webber, J. (2009). Seek and destroy – Phytophthora update. The Horticulturist 18 (4), 5-7.

Webber, J., Hendry, S., MacAskill, G. and Steele, H. (2004). Dutch Elm Disease Today. Farm Woodlands Newsletter 5 (Autumn 2004), 3.

Inman, A. and Webber, J. (2004). A threat to our trees: Phytophthora ramorum (and its long lost cousin). Arboricultural Association Newsletter Issue128, 20-23.

Evans, H. and Webber, J. (2004). Pests and diseases. In: Forest Research Annual report and Accounts 2003-2004 (PDF-4239K), pp. 30-39. The Stationery Office: Edinburgh.

Webber, J., Gibbs, J. and Hendry, S. (2004). Phytophthora Disease of Alder (PDF-1350K). Information Note 6 (revised). Forestry Commission: Edinburgh.

Other publications (to 2003)

Publications 1981 to 2003 (PDF-63K)