Olive farmers in southern Italy are dealing with a serious outbreak of olive quick decline syndrome, a new disease with symptoms that include leaf scorching, twig and branch dieback and, ultimately, tree death. In October 2013, the plant pathogen Xyllela fastidiosa was found for the first time ever in Europe and appears to be associated with the disease.

This has California researchers worried and baffled. The bacterium Xyllela fastidiosa has been present in the state for more than 100 years and can sometimes be found in olive trees. Trials conducted by USDA and UC researchers from 2008 to 2011 showed that strains of the bacterium found in California did not cause disease in olives.

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