Douglas M. Main wrote about the detection of huanglongbing disease in Southern California in the New York Times Green Blog.  

The greatest immediate threat may be to the homeowners of Los Angeles County, 60 percent of who have a citrus tree in their yard, said Elizabeth Grafton-Cardwell, UC Cooperative Extension specialist and research entomologist in the Department of Entomology at UC Riverside and director of Lindcove Research & Extension Center. 

The citrus greening bacteria probably spread from the cutting of budwood illegally brought in from outside the country, the article says Grafton-Cardwell said.