The plants slowly suffocate, wither and dry out. They die en masse, the leaves fall and the bark turns gray, creating a sea of black and white. Since scientists first discovered it Xylella fastidiosa in 2013 in Puglia, Italy, it killed a third of the region's 60 million olive trees - which once produced almost half of Italy's olive oil - many of which were centuries old. Farms stopped producing, olive mills went bankrupt and tourists avoided the area. Because there is no known cure, the bacterium has already caused damage costing approximately 1 billion euros.
"Most of the territory was completely destroyed," said Donato Boscia, plant virologist and principal researcher on Xylella at the Institute for Sustainable Plant Protection in Bari.
Ten years later, still nowhere near a solution, the threat to European plants from Xylella and other diseases is only increasing: in February 2024, scientists from Puglia found another Xylella subspecies, which had destroyed American vineyards and never before was discovered in Italy. For many farmers, scientists and regulators, the disease is emblematic of a much broader problem: the EU's difficulty in curbing the introduction of devastating new plant diseases, despite regulatory efforts over the past decade. New data released to the Guardian shows that dozens of newly introduced disease outbreaks are being discovered in the EU every year, even as farmers and scientists struggle to contain previously introduced pathogens. As the climate warms, scientists warn the problem will only get worse.
Data shows that across the EU, outbreaks of newly introduced plant diseases have continued unabated between 2015 and 2020, at an average rate of 70 per year, despite regulations introduced in 2016 to stop their spread. While a number of Member States have taken steps to prevent and contain outbreaks, scientists, plant epidemiologists and agronomists say this is still insufficient.
"I don't understand why we have learned virtually nothing after Xylella," says Pierfederico La Notte, an Italian plant epidemiologist.
Import system - open or closed?
On a sweltering June morning in 2023, Paolo Solmi, a phytosanitary inspector at the port of Ravenna in northern Italy, tells his team to open the first of 28 containers of Egyptian potatoes to check that day. They fill bags with 100 potatoes each before taking them to the laboratory for standardized EU testing.
"Once these checks have been passed, the goods can move freely within the European Union," says Solmi.
The EU has an open import system: anything that is not known to be harmful can enter. Some countries, such as New Zealand and Chile, have opted for a closed system: everything is considered guilty until proven guilty.
There are indications that the Xylella bacteria came from Latin America and was most likely brought through the Netherlands via ornamental coffee plants. Between 2005 and 2014, approximately 30 billion rooted and unrooted plants, cuttings, bulbs and tissues entered Europe from third countries, mainly via Dutch ports.
According to Alberto Santini, forest pathologist at the Italian National Research Council, such an open system has allowed in an alarming number of plant pests and diseases from third countries.
"If you know your enemy, you can try to prevent him from entering your country," says Santini. But, he added, many pathogens are harmless elsewhere because ecosystems evolved with them. While Xyllela may not have affected Costa Rica's coffee plants, it did thrive when it encountered the defenseless southern Italian olive trees.
We are constantly introducing new organisms...climate change will make them increasingly difficult to manage
Pierfederico La Notte, plant epidemiologist
The EU introduced new regulations in 2016 to better manage what comes in and how, and to tackle outbreaks quickly. Yet, with so many ports of entry, scientists and regulators cannot keep up with incoming volumes. Trioza erytreae, a sap-sucking pest, endangers Portuguese citrus fruits; a bacterium that infects carrots and celery has sparked concern across the continent; And Hymenoscyphus fraxineus killed ash trees in Poland. Many scientists fear the spread will be aided by the climate crisis, which is making Europe a warmer, more hospitable place where foreign plant pests can thrive.
"With the current system in Europe, we are constantly introducing new organisms," says La Notte. "In the context of climate change, it will become increasingly difficult to control it."
Data provided to the Guardian by Wopke van der Werf and Hongyu Sun, researchers at Wageningen University and Research in the Netherlands, shows that there have been 1,720 recorded outbreaks of non-native plant diseases in the EU between 1975 and 2020, with Italy, France and Spain are responsible for half of it. 2018 was the worst year, with 115 known cases.
The data comes from the European and Mediterranean Plant Protection Organization (EPPO) database, which records where non-native plant diseases - outbreaks caused by non-native insects, pathogens and nematodes - are found for the first time or in a new region within the union. That data is likely an underestimate: EPPO collects new findings by scanning the scientific literature and obtaining official pest reports from the national plant protection organizations of the Member States. The reports are therefore limited to each country's responsiveness and interest in investigating an unusual pest sighting.
According to La Notte, a number of crops - such as grape vines - are heavily regulated. But many other plants, especially ornamental plants, are treated more leniently, making them potential carriers of non-native plant pests. Wooden pallets, internet plant sales and travelers taking banned plants or fruits are all responsible for bringing in diseases, according to several researchers interviewed for this story.
A long trading history
For some countries, such as the Netherlands, open trade in plants is a core part of their history and economy - and they have resisted increasing regulation. Christian Linden, the founder and CEO of IBH Export, walks around his 14,000 square meter warehouse at the Aalsmeer flower auction house in the Netherlands. He imports cut flowers and potted plants, mainly from Turkey and East Africa, and redistributes them throughout Europe.
Linden says he doesn't know much about pathogens or insects coming in through the plant trade, but isn't concerned because phytosanitary authorities are "very strict." He thinks the 2016 Plant Health Regulation has provided better protection for the EU, and points to the introduction of plant passports, which did not exist when Xylella arrived in Italy. Today, he adds, if a customer finds a disease or insect on an imported plant, the entire shipment is tracked down and destroyed.
"If it is necessary to protect the environment, you should do it," he says.
John Van Ruiten, former director of Naktuinbouw, the Dutch horticultural inspection service, says that the controls on imported material are strict. However, he admits that it is difficult to detect everything - insects, symptoms of bacteria or viruses - especially during a visual inspection: "It is impossible for inspectors to know about all diseases in all products."
According to international protocols, only a sample of approximately 2% of imported plants is checked for the presence of symptoms, according to the Dutch Food and Consumer Product Safety Authority (NVWA). Given the number of plants entering through the main EU ports, it is "possible that new species may be introduced".
The NVWA says it believes that the Netherlands has a robust control system. For example, once certain live plants cross the border and enter a nursery, the phytosanitary inspector checks them again after two weeks to ensure that they do not carry any latent diseases.
According to Van Ruiten, the burden of preventing diseases should not fall entirely on the shoulders of the importers. He says exporting countries in Africa, Asia and Latin America must also carry out proper controls.
Balancing costs and benefits
In the port of Ravenna, phytosanitary inspector Solmi recognizes the challenge. "Europe was created around the movement of goods, capital and people," he says. "Our mission is to do our best within the open phytosanitary system, because there is currently no alternative."
But while the economic costs of what the EU could lose in trade are significant, so too is the price of damage caused by alien pests and diseases. How do you put a price on a lost bunch of ash trees?
"The main economic problem is that data is quite scarce," says Françoise Petter, former deputy director at EPPO. The costs and benefits of a closed system have not been calculated, and it is unknown whether the losses from a slower trading system would be offset by the retained value of EU agriculture and biodiversity.
"We never tried to make a complete comparison with a closed system," says Petter. "That's a bit depressing, isn't it?"
This article was produced with the support of Journalismfund Europe Find more extinction age coverage and follow biodiversity reporters here Phoebe Weston And Patrick Groenveld on X for all the latest news and features
