The fatal citrus disease responsible for Florida's significant production declines continues its spread across southern California as nearly 1,700 trees have been confirmed with the bacterial infection known in California as Huanglongbing (HLB). By law those trees have all been removed and destroyed.

The latest discovery of an infected residential tree by the State of California is in the city of Montclair, between Ontario and Pomona. The new find will expand the state's main HLB quarantine zone eastward towards a smaller zone that encompasses Riverside, the University of California campus there, and it's citrus research grove.

California officials announced the new 93-square-mile quarantine zone bordered by the I-210 freeway, Hwy. 57, Ontario International Airport and the Chino Airport. The quarantine prohibits movement of all citrus nursery stock or plant materials from the zone. Provisions exist to allow movement of commercially cleaned citrus and packed citrus. All other forms of citrus, to include fruit grown in residential yards, cannot be removed from the property upon which they were grown.

To date over 1,100 square miles of urban landscape in four counties is under citrus quarantine rules that restrict the movement of fruit and nursery stock. The largest concentration of HLB finds is in Orange County, where more than 1,200 trees were confirmed with the disease. Over half those finds were in the cities of Garden Grove and Anaheim. Conversely, the city of Hacienda Heights, where California's first HLB find was detected in 2012, has seen two trees test positive for the disease.

Huanglongbing is a bacterial disease transmitted by the Asian citrus psyllid, a tiny insect that feeds on new shoot growth. That feeding activity can transmit the bacterium from the pest to the plant. Insects feeding on infected plant material can then carry the disease and transmit it to other citrus plants. The disease eventually causes fruit to ripen unevenly, create a bitter taste within that fruit, and lead to the death of the tree.

The only confirmed cases of HLB in California have been in residential trees in southern California.