The European Food Safety Authority (ESFA) said computer modelling has helped understand how Xylella fastidiosa spreads, but there is no cure for infected plants.
Experts describe Xylella as one of the “most dangerous pathogens worldwide”.
The disease was first detected in 2013, when an outbreak struck the southern Italian region of Puglia, killing masses of ancient olive trees.
More than a million trees, or 10 per cent of the total in Salento, at the southern end of Puglia, are estimated to have been infected.
Experts are yet to discover where the disease came from.
The deadly disease has since spread to other European countries, including Spain, France and Portugal.
The EFSA warned in its latest report that strains of the bacteria could potentially spread further throughout Europe, including into the northern areas.
Experts said that the trees may be infected for up to a year before signs begin to show.
Xylella does not harm humans but can kill over 200 plant types, including fruit trees and grape vines.
EU emergency control measures have been implemented in all of the affected areas, despite some resistance from local farmers to the massive tree culls ordered as part of the plan to tackle the disease in southern Italy.
The EFSA stressed in its report that control measures are “crucial” until a cure can be found.
Globally, the EU is the largest producer and consumer of olive oil.
According to the European Commission, the EU produces 73 per cent and consumes 66 per cent of the the world’s olive oil.
Italy is the second-largest producer of olive oil after Spain.
