Whisper the words Xylella fastidiosa and the British horticultural industry will break out into a collective sweat. Xylella is a fast-spreading bacterium that has wiped out olive groves in Italy and is attacking swaths of fruit and ornamental plants across western Europe. Its range of more than 650 host plants includes trees such as oak, elm, olive and plane, and a long list of garden favourites including lavender, rosemary, hebe and jasmine.
It is not yet in the UK, but it if does sneak in it could be devastating, says Raoul Curtis-Machin, director of horticulture at the Royal Botanic Garden Edinburgh (RBGE). An outbreak of Xylella fastidiosa “could lead to teams descending on gardens to rip out and burn many different plants in all the gardens within 100m of the outbreak,” he says. “This disease could have a massive impact on the British landscape.”
It’s just one of the dangers to garden life that the UK Department for Environment Food and Rural Affairs aims to educate the public about during the third National Plant Health Week. From May 8 to 14, coinciding with the UN’s International Day of Plant Health on May 12, there are online resources such as activity sheets for children to show how we can all grow plants safely.
“Like in a supermarket where you can see where food is from and might decide not to buy it, Defra wants people to take more responsibility and ask where their plants come from,” says Matt Elliot, plant health and biosecurity scientist at RBGE.
Plant Health Week is part of Defra’s new five-year plant biosecurity strategy to prevent and contain pathogens. Keeping safe requires a combination of government, industry, import controls and public vigilance, says Simon Toomer, curator of living collections at Royal Botanic Gardens, Kew.
Xylella is not the only nasty lurking in the wings. There are 1,406 pests and diseases on Defra’s UK plant health risk register. These include the emerald ash borer (Agrilus planipennis); Asian and Citrus longhorn beetles (Anoplophora glabripennis and A chinensis); pine processionary moth (Thaumetopoea pityocampa); and oak and plane wilt (Ceratocystis fagacearum and C platani).
Some deadly pests have already sneaked in. The oak processionary moth is afflicting oaks in London and the surrounding area and can cause allergic reactions in people. It is being contained in south-east England but climate change could jeopardise that. “As our climate warms, some imported pests and diseases will extend their range,” says Toomer. “We are controlling it but its band is moving outwards and upwards each year.”
Non-native pests and diseases are unintentionally imported into the country on infected plants and seeds or hidden inside timber packaging. Oak processionary moths have been found on trees imported from the Netherlands and an outbreak of Asian longhorn beetle (Anoplophora glabripennis) in Kent in 2012 arrived in wooden packaging from China. It is thought to have been eradicated after the destruction of thousands of local plants.
The threat is a byproduct of world trade, and plants are big business. Defra statistics show that In 2021, trade in plants and plant commodities (including timber, fruit and veg) was worth nearly £16bn, of which £14.5bn was imported (92 per cent).
“The problem has increased in the past 20-30 years because of gardeners wanting more exotic plants. Now you can buy a vast array of plants from anywhere in the world,” says Elliot.
And far too cheaply, says Curtis-Machin. “If you think about the price of a plant, it’s ridiculously cheap when you consider the amount of work that’s gone into it,” he says. “I can’t think of any other product that has that amount of love and time spent on it that’s so cheap. We want plants for instant gratification and we’re all to blame because we’ve got into that ‘pay your money and get your instant garden’.”
The golden rule is to only buy plants from reputable suppliers, whether on the internet or at a retail outlet. If they are not grown by a nursery on-site, look for a plant passport. By law, plants transported around Britain must have a passport so that any disease outbreak can be traced back to its source. Legally imported plants will also have a phytosanitary certificate confirming that they are free of infection.
If you spot any pest or disease on a plant that you cannot identify, check out the RHS website on pests and diseases, including non-native ones. If worried, report your sighting to the Animal and Plant Health Agency ([email protected]).
You should never smuggle back plants yourself from abroad. “I’m sure people still bring plants back from holiday. The really risky one is potatoes. You’ll hear of people bringing back potatoes to grow on their allotment,” says Elliot. “They could introduce pests and diseases into the UK which could be devastating. You shouldn’t bring back anything at all.”
There is a post-Brexit ban on importing seed potatoes into the UK, and smuggling any plant can result in criminal penalties, including a fine.
Gardeners also need to take care when swapping or moving plants, says Toomer. “In this part of the world [south-east England], people have given up on their box because it’s been wiped out by the box tree caterpillar. There are now pockets of it elsewhere because people took bits of box from their gardens and planted it in other gardens,” says Toomer. “You need to know what pests and diseases affect a particular plant and what is in your area.”
“If you can buy locally, that’s perfect,” says George Plumptre, chief executive of the National Garden Scheme. “A lot of our members sell plants they have grown themselves or from a local nursery. The thing about travel is that it greatly increases the risk from imports.”
Others agree. “We’d like to see the government nurturing a homegrown plant industry,” says Curtis-Machin, suggesting tax breaks for nurseries that sign up to Plant Healthy, a voluntary biosecurity certification scheme that verifies plant passports. “The industry wants to do the right thing but it’s looking at its bottom line.”
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