In addition to once again ravaging olive trees in Italy this spring, the deadly Xylella plant disease is showing signs of spreading further in the Mediterranean olive growing regions.

In a containment zone in Salento, in southern Italy’s Puglia region where the disease wiped out hundreds of olive trees during its initial impact, the number of trees infected with the Xylella fastidiosa bacterium had quadrupled, according to The Olive Oil Times.

The bacterium had spread from its containment zone in the agricultural area of Valle d’Itria to the coastal plain of the Piana degli Olivi Millenari, which was home to some of the oldest olive trees in Puglia, and there were fears that it would make its way further inland.

Elsewhere in the Mediterranean, Spanish authorities had reported that they had found a Xylella infected olive tree on Spanish mainland near Madrid.

The disease had earlier been discovered on the Balearic island of Mallorca, according to Xylella expert Alexander Purcell from the University of California at Berkeley.

“Subsequently, other strains of Xylella were found in all of the other Balearic Islands, indicating that the bacterium must have been independently introduced at least several times,” he told The Olive Oil Times.

Xylella had also made its first ventures into France this spring, with the Corsica chapter of the Interprofessional Union of Oleiculturists reporting in April that olive trees on the island had been infected.

The disease was found in Corsica and in ornamental plants in the French Riviera earlier in 2015 but, at the time, it had not yet spread to olive trees.

Xylella was introduced into Europe through tropical plant imports from Central America, where it has attacked, among others, citrus, coffee, grape and alfalfa crops.

According to the International Olive Council, the Mediterranean Xylella outbreak led to a global drop in olive oil production last year.