Xylella fastidiosa is a disease causing bacterium that affects a wide range of important woody plants and broadleaved trees. It invades the xylem vessels that transport water throughout plants and causes symptoms that range from leaf scorch to tree dieback and death. In the natural environment it is transmitted by xylem-fluid feeding insects such as leafhoppers. Until recently the bacterium was only known in the Americas and Taiwan, but an outbreak on olive trees in southern Italy was confirmed in 2013. Affected shrubs were also found in France in 2015. In Italy, the bacterium is apparently causing the rapid decline of olive trees over a large area and is under emergency measures. It has not yet been found in the UK and measures are in place to protect our trees.