County Agricultural Commissioner Henry Gonzales announced that an Asian citrus psyllid was found in the Spanish Hills neighborhood last Thursday.
Ventura County is under quarantine for the tiny pest.
The California Department of Food and Agriculture was expected to begin treatments with two kinds of pesticides after surveying the area over the weekend.
The Asian citrus psyllid can carry the huanglongbing disease. The untreatable disease has yet to be found in California, but it has ruined crops in several southeastern U.S. states.
The Associated Press contributed to this report.