Documents: Special Interest: Gardening In England:

Global Plant Trade Poses Increased Risk of Alien Diseases

attacking gardens and the countryside
by Georgie Webb
August 31, 2008

Alien pests and diseases inadvertently imported on exotic plants are threatening the plants in our gardens and across the countryside, according to a report launched by a scientific working group led by the Royal Horticultural Society (RHS).

The number of plant disease outbreaks is up by 60% on last year*. Increased global plant trade, coupled with evidence of rapid climate change, suggests that the problem will multiply.

Recent Defra reports have highlighted the worrying spread of disease on rhododendrons in the south west of England caused by Phytophthora ramorum and Phytophthora kernoviae, while many other diseases, including Cylindrocladium buxicola, [box blight] which is responsible for the destruction of native box hedges, and Ophiostoma novo-ulmi, [Dutch elm disease] are well known to the working group.

The report, Non-native diseases and the future of UK gardens, is being published today. It proposes that the horticultural industry worldwide develops effective systems to manage the risks that growing and trading of ornamental plants are now creating.

Suggested features of such a system would be similar to those, driven by the supermarkets, that are now familiar in relation to food assurance schemes. The report suggests that new quality assurance systems, driven by a voluntary code of conduct, could sit alongside the current UK plant inspection programme and offer further reassurances to the plant buying public. In 2005, £870 million was spent on imported plants by the British public, three times as much as in 1988. The current inspection scheme only applies to plants known to play host to diseases and does not provide the opportunity to capture evidence of new diseases symptoms throughout the plant production, transportation and selling process.

Dr Simon Thornton Wood, Director of Science and Learning at the RHS, explains, “The current plant inspection programme works exceptionally well for diseases we already know about. But it is the unknown diseases on plants that would not normally be considered problematic that are the real cause for concern. Phytophthora kernoviae and P. ramorum entered the UK because they were not known about and so not checked for. They have wreaked havoc with cultivated rhododendrons and now threaten to spread to our native heath land.

“However, an industry code of conduct could provide the answer, with every stage of the production and transport process managed with disease risk in mind. We would then be able to avoid another situation like sudden oak death or Dutch elm disease that has changed the face of the Britain’s countryside.”

Striking the balance between plant health and providing the variety of plants that inspire this nation of gardeners, is at the forefront of the RHS’ mind. The UK’s leading gardening charity believes that consumer awareness could be the key to ensuring that a code of conduct, underpinning true quality assurance, is developed by the plant importing trade.

Dr Simon Thornton Wood continues, “Working together gardeners can help the RHS to track the emergence and spread of pest and disease problems and together we can all take responsibility for the health of our gardens and the wider environment. Everyone has an interest in ensuring that high-quality, disease-free plants arrive at our shores and reach our gardens.”

For help and advice on identifying plants pests and diseases visit and to view a copy of Non-native diseases and the future of UK gardens contact the RHS press office on 020 7821 3044. A DEFRA consultation on the problem of Phytophthora was launched at RHS Garden Wisley on 15 July 2008.

• Phytophthora [fi-toth-or-a]

• Members of the RHS led Working Group regarding Non-native diseases and the future of UK gardens Chair: Professor David Ingram, Honorary Professor, Universities of Edinburgh and Glasgow. Formerly RHS Professor of Horticulture.

Members: Professor Clive Brasier, Visiting Professor, Imperial College, University of London.

Tim Briercliffe, Director of Business Development, Horticultural Trades Association

David Gilchrist, Horticulturalist and Consultant to the HTA

Dr Nicola Spence, Head, Plant health Group, Central Science Laboratory, York

Professor Jeff Waage, Director, London International Development Centre

Secretary: Dr Chris Prior, Former Head of Horticultural Sciences, RHS

Observer: Dr Emma Frow, Research Fellow, Economic and Social Research Council, Genomics Policy and Research Forum, Edinburgh

• *Based on the number of enquiries to the RHS advisory service from RHS members between July and September 2006 and the same period in 2007 - Pathology Section Yearly Review 2007, RHS

• For information on Defra reports visit

• In 1988 the UK imported £285 million worth of ornamental plants. In 2005 this figure had trebled to £870 million (DEFRA Basic Horticultural Statistics) Further examples of invasive, non-native diseases -

• Ophiostoma novo-ulmi caused the death of 20 million young elm trees during 1970’s Dutch elm epidemic.

• In Portugal and Spain, the cork oak tree is currently under threat from Phytophthora cinnamomi, which has already caused environmental destruction elsewhere in the world.

• Cryphonectria parasitica is attacking the American chestnut tree across the north east coast of the country.

About the RHS

The RHS believes that gardening improves the quality of life and that everyone should have access to great garden experiences. As a charity we help to bring gardening into people’s lives and support gardeners of all levels and abilities; whether they are expert horticulturalists or children who are planting seeds for the very first time. RHS membership is for anyone with an interest in gardening. Support the RHS and secure a healthy future for gardening. For more information call: 0845 130 4646, or visit

RHS Registered Charity No. 222879/SC038262

  • New Eden
  • Kids Garden
  • Plant a Row Grow a Row