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News article12 November 20193 min read

Monitoring the impacts of Xylella fastidiosa

Xylella fastidiosa has a devastating impact on centuries-old olive trees in southern Europe
© Cesare Palma –

The plant bacterium Xylella fastidiosa severely damaged an estimated 6.5 million olive trees in southern Italy by 2017, and could cost the EU billions of euros in production and job losses.

These are some of the latest JRC findings presented at the Second European Conference on Xylella fastidiosa in Corsica last month.

Around 350 plant health specialists from around the world attended the conference for two days of intense discussions on how science can help find solutions to the plant pest that is causing environmental and economic damage across Europe.

Hundreds more followed proceedings via a special live web streaming of the event.

JRC findings

JRC scientist Pieter Beck explained how the JRC uses remote sensing to detect, monitor and map olive orchards infected by Xylella fastidiosa in Apulia in southern Italy. Using satellite data and weather data, his team estimated that about 6.5 million olive trees in the area had been severely damaged by 2017.

The findings showed how the Xylella fastidiosa epidemic in Apulia is continuing to grow, and showing no signs of slowing down.

While the situation is clearly dire now, other JRC research presented at the conference by JRC scientist Berta Sanchez shows that, unless it is contained, Xylella fastidiosa could cause damages in the order of billions of euros, posing a threat Europe's economy and biodiversity.

These estimates were part of a JRC-EFSA study on priority pests identified under the EU’s new Plant Health Law (Regulation (EU) 2016/2031).

Xylella fastidiosa

The bacterium Xylella fastidiosa is a plant pathogen transmitted by insects that feed on the xylem fluid of plants.

It is a quarantine pest in the European Union (EU), which means suspected sightings must be reported immediately to the plant health authorities.

Rapid spread in southern Italy

Since it was first detected in Europe near Gallipoli in 2013, Xylella fastidiosa has spread to other zones of Apulia, and caused a rapid decline in olive tree plantations.

Google Street Views of the same place near Gallipoli in 2011 (top) and 2015 (bottom), showing the devastating impact of Xylella on olive trees
© Google Maps/Google Earth

JRC mapping of the area severely affected by Xylella

The JRC set out to measure the regional impact of Xylella by monitoring the extent and progress of the damage to olive orchards across Apulia using remote sensing and weather data.

Using the free and open Earth Observation data from the year 2000 to 2017, the researchers monitored 27,188 large (greater than 12.5 ha) olive orchards - which represent 80% (2,261 km2) of the orchards in the area officially declared infected by Xylella fastidiosa in Apulia. They then validated their findings against official monitoring data and independent field observations of damage to olive trees.

The geographical distribution of ‘severely damaged’ olive groves observed from 2012 to 2017.
The geographical distribution of ‘severely damaged’ olive groves observed from 2012 to 2017. Colour: areas where the disease has been present since the year of detection; Grey: apparently healthy orchards, where the new method did not detect severe damage
© EU, 2019

By 2017, the researchers detected severe damage in large orchards covering 538 km2. Extrapolating this figure to 100% of the area, the total severely damaged area is estimated to be closer to 650 km2, or about 6.5 million olive trees (as orchards have on average around 100 trees per ha in this region).

Most worryingly, the area with severe damage is growing steadily, with no sign of this growth slowing down.

The researchers hope to be able to update these figures to 2019 by the end of this year, once this summer’s weather data become available.

Economic impact of Xylella fastidiosa

A recent report by the JRC estimates that Xylella fastidiosa full spread could ultimately cost the EU over €5.5 billion per year due to loss of production, with potential export losses of €0.7 billion per year.

The researchers further found that, if Xylella were to fully spread across the EU, it could affect over 70% of the Union’s production value of olive trees older than 30 years, and 35% of the younger trees. This could put nearly 300,000 jobs involved in olive trees, citrus, almonds and grapes production at risk.

It is hoped that, by working together and sharing the latest scientific knowledge of the risk posed by Xylella fastidiosa, the scientific community can help policymakers tackle this dangerous and devastating pest.

Further information

Related Content

Second European Conference on Xylella fastidiosa

2nd European conference on Xylella fastidiosa - Pieter Beck Youtube

Estimating the economic, social and environmental impacts of EU priority pests: a joint EFSA and JRC project with a focus on Xylella fastidiosa

EFSA press release: Xylella fastidiosa: ‘Together we can find solutions’

Plant Health: prioritising the fight against 20 quarantine plant pests on the EU territory

JRC report: The Impact Indicator for Priority Pests


Publication date
12 November 2019