This could affect the consumer price for olive oil.
A potentially deadly disease affecting olive trees in Europe could take a huge economic toll in the next five decades, researchers have said.
A new study suggests losses could be as high as five billion euros (£4.2 billion) for Italy, 17 billion euros (£14.5 billion) for Spain, and two billion euros (£1.7 billion) for Greece if nothing is done to stop the spread of the disease and olive groves are not replanted.
The three countries account for 95 percent of European olive oil production.
The findings, published in the journal Proceedings of the National Academy of Sciences (Pnas), are based on an economic modelling of the impact of the disease caused by Xylella fastidiosa, which is considered to be one of the most dangerous plant pathogenic bacteria worldwide and is spread by insects known as spittlebugs.
The study authors wrote: "Even under slow disease spread and the ability to replant with resistant cultivars, projections of future economic impact in affected countries run in the billions of euros.
"Our findings highlight the importance of minimising disease spread and implementing adaptation measures in affected areas."
The researchers said drastic action, which would also include felling seemingly healthy trees, would be required to stop the spread of the disease known as olive quick decline syndrome.
Regulatory measures were enacted in Italy after a similar bacterial strain destroyed around a million trees in 2013.
A team led by Dr Kevin Schneider, from Wageningen University in the Netherlands, developed a bioeconomic model of Xylella's future spread and impact.
They factored in the different cultivation systems in each of the countries and modelled economic losses under a scenario in which all growing ceased due to tree death. This model was then compared with another scenario in which replanting with resistant varieties occurred.
Results showed that, if measures are taken, the overall economic impact could be lowered to around 1.6 billion euros (£1.3 billion) in Italy, with proportionally similar benefits in Spain and Greece.
The researchers also believe the measures taken to protect olive groves could increase the costs of olive oil for consumers.
The team wrote in their paper: "Most olives are used as an input for processing into olive oil. In turn, the simulated price increase would result in higher costs of production for oil processors. This could affect the consumer price for olive oil."
Nilima Marshall is the PA science reporter.