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Preventing plant disease

Preventing plant disease

Professor Nicola Spence


Professor Nicola Spence says designers need to help stop Xylella 


We are an island nation. Yet, in a world of ever-increasing global trade and travel, foreign threats to the health of plants overseas are threats to our plants too. As the UK’s Chief Plant Health Officer, it is my job to work with the horticulture sector to keep these threats at bay and our plants and trees safe.

Right now we are working together to protect against an aggressive bacterial disease which is being found in some parts of Europe: Xylella fastidiosa. Xylella, native to South America, clogs up the xylem – the arteries that carry water – starving the plant and drying it out. This results in leaf scorch, dieback and, in some cases, the death of the plant.

In recent years, the disease has made its way into Europe. In Italy, more than a million olive trees have been affected, while in the Balearic Islands and southern France, thousands of plants and trees have been devastated, with a range of shrubs, like Polygala, as well as rosemary and lavender all affected.

If the disease were to arrive in the UK, the implications would be significant and we would need to take swift action. There are more than 150 different types of trees and plants that can host the disease and, in line with the EU-wide protocol, all hosts within 100m of any plant identified to have the disease would need to be destroyed and the surrounding area treated. The trading and movement of potential hosts would also be restricted within 5km of where any infected plants have been found.

This would clearly have an enormous impact on nurseries and plant businesses. So, how do we protect ourselves? The first line of defence is to ensure that plants infected with Xylella never begin the journey towards our shores. This job is in the domain of policy makers and in September, the Environment Secretary Michael Gove wrote to the European Commission to encourage the introduction of more rigorous checks and stronger import, plant passporting and traceability requirements for high-risk hosts before movement from the exporting country. These increased protections were secured in a vote in the European Commission in October.

At home, our national legislation requires the notification of high-risk imports, allowing the Animal and Plant Health Agency to watch out for key threats and carry out targeted inspections. Within the UK we have a surveillance programme, targeting imports and businesses trading in hosts from within the EU, as well as inspections in the wider environment. Leaving the EU will provide an opportunity to examine how we can introduce stricter biosecurity measures on imports from Europe in cases like this where there is a disease risk.

But government cannot act on this alone, and garden designers have a big role to play. The key way you can help is by avoiding purchasing high-risk Xylella host plants. The key plants to avoid are Polygala myrtifolia, olive, lavender, rosemary, almond and Nerium oleander, but a full list of the risk species can be found on the Defra Plant Health Portal.

You may have already noticed that the supply of these plants has been affected. Following an emergency meeting, a large group of plant retailers has committed to avoid purchasing any host plants originating from regions where Xylella is present. Government is committed to working with trade associations and others to provide the most up-to-date information to help inform good purchasing choices and biosecurity. Please check for Xylella initiatives from organisations that you are members of, and check the Defra Plant Health Portal for further advice and updates.

Xylella has caused devastation to plants and trees in Europe. So far it hasn’t been found in the UK. Let’s work together to keep it that way. 


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