Sweetgum dieback and leaf scorch of purple-leafed plum are two new diseases of southern California landscape ornamentals. Samplings were conducted in 2003 and 2004 and 28 of 105 sweetgum (Liquidambar styraciflua) and 38 of 62 purple-leafed plum (Prunus cerasifera) plants tested positive for Xylella fastidiosa by enzyme linked immunosorbent assay. In all, 3 strains of X. fastidiosa were isolated from sweetgum and 13 from purple-leafed plum. All sweetgum strains and some purple-leafed plum strains grew on PW but not PD3 media. Strain PC045 from purple-leafed plum and strain LS022 from sweetgum were inoculated into their original hosts in addition to almond, oleander, and grapevine plants. Sweetgum plants also were inoculated with strains causing Pierce’s disease, almond leaf scorch, and oleander leaf scorch. Strain PC045 caused symptoms in purple-leafed plum and almond plants within 6 months, and the pathogen was recovered from 93 and 100% of inoculated plants, respectively. Inoculation of grapevine and oleander plants with PC045 did not result in disease or recovery of the pathogen. In all, 5 of 25 sweetgum plants inoculated with LS022 showed symptoms after 9 months, and the pathogen was recovered from 3 of these plants. Inoculation of grapevine, oleander, and almond with LS022 resulted in no disease or recovery of the pathogen from the plants. A strain of Pierce’s disease, a strain of oleander leaf scorch, and two strains from almond did not cause disease in sweetgum. These results confirm the role of X. fastidiosa strains as pathogens of purple-leafed plum and sweetgum, and that strains from sweetgum are unique in their host range.