The Chico Enterprise Record has an article, written by the Deputy Agricultural Commissioner of Butte County, California, about invasive olive trees - true olives (Olea spp.), not Russian or autumn olives (Elaeagnus spp.). The Deputy Ag Commissioner notes that abandoned olive groves in California have become vectors for crop pests, like the Olive fruit fly (Bactrocera oleae), and these pests are threatening active olive orchards. The fruits of the abandoned trees are also being dispersed by birds, and some trees have been found in wild areas.
A story featured on the ISW back in April of this year noted that the olive trees in Australia have gone feral as well.