The California Department of Food and Agriculture said on Wednesday that 178 square miles in Tulare County have been quarantined following the detection two weeks ago of six Asian citrus psyllids around Porterville.
The quarantine prohibits the movement of nursery stock out of the area and requires citrus fruit to be cleaned of leaves and stems. Farmers must also spray their trees with insecticide.
Agriculture department spokesman Steve Lyle said the psyllids did not carry the deadly bacteria that has decimated Florida's citrus industry.
Similar quarantines are now in place in Ventura, Santa Barbara, San Diego, Imperial, Orange, Los Angeles, San Bernardino and Riverside counties.