Summer 2012: Citrus greening in California

Regional Report San Diego and Riverside Counties by James A. Bethke

Huanglongbing (HLB), or citrus greening, has finally made its way into California. To date, a single tree and a single Asian citrus psyllid (ACP) have tested positive for the disease, and the anticipated regulations for citrus production and retail nurseries are now in effect. Some of these regulations are still under review by the California HLB Task Force Science and Technology Advisory Committee, but every nursery that carries citrus should take note because subsequent spread is likely. At present, about 4800 trees at 18 facilities (production and retail) are on indefinite hold.

The California Department of Food and Agriculture declared a state interior quarantine (#3439 HLB Disease) as of April 12, 2012, and the declaration includes information on the disease, the area quarantined, the regulated articles, and movement restrictions. An approximate five-mile circle has been drawn around the infested tree, and action is being taken within the circle. No plants in the Rutaceae family can move out of quarantine. All Rutaceae plants within 800 meters of the infested tree have been tested for HLB, and so far all have tested negative. In addition to the surveys for HLB, all Rutaceae plants within 800 meters have been treated in adherence to quarantine protocol.

The present HLB infection likely occurred through the movement of infected tissues from Asia that were grafted onto a backyard tree in Hacienda Heights, which has since been removed and destroyed. A full investigation is in progress, and other trees associated with the infected tree have been identified. So far, they have tested negative for HLB. If the historic pattern of movement of HLB by infected psyllids remains consistent, then HLB from the tip of Baja or central   Mexico will eventually establish in San Diego County and other parts of California.

In anticipation of an HLB find, the CDFA has been preparing further restrictions on citrus nursery stock and its production. In short, to protect the citrus production industry, all citrus must now be produced in protected culture. Screenhouses must be constructed under specified construction standards that include a 100-foot buffer from any Rutaceae plants, as well as screens that exclude ACP, air curtains or positive airflow, and self-closing doors. The facility must be maintained pest free, with detection trapping and records that demonstrate the facility is free of psyllids. The facility must be inspected for breaches, and trapping or suction monitoring for ACP must occur regularly. Source citrus must originate from APHIS-approved State certified clean stock, and all citrus within the facility must be treated at least 30 days and no later than 90 days prior to shipment.

Unfortunately, a recent scientific paper demonstrates that edible fig (Ficus carica) is an ACP host. How this will affect the genus Ficus is still not clear, but edible fig will most likely be added to the list of regulated articles, further complicating the situation for the nursery industry. The HLB Task Force Science and Technology Committee is reviewing the literature and will soon make recommendations concerning this issue to the CDFA.

See below for important information from some of the pertinent web sites: 

CDFA Plant Quarantine Manual: #3439 HLB Disease: http://pi.cdfa.ca.gov/pqm/manual/pdf/423.pdf (includes map of the quarantined areas of Los Angeles and Orange counties).

United States Department of Agriculture Animal and Plant Health Inspection Service (APHIS) Plant Protection and Quarantine: Interstate movement of citrus and other Rutaceous plants for planting from areas quarantined for citrus canker, citrus greening, or Asian citrus psyllid:

http://www.aphis.usda.gov/plant_health/plant_pest_info/citrus/downloads/interstate-mvmnet-protocol.pdf

James A. Bethke
Farm Advisor, Nurseries and Floriculture
UC Cooperative Extension San Diego, North County Office
151 E. Carmel St., San Marcos, CA 92078
(760) 752-4715 phone
(760) 752-4725 fax
jabethke@ucdavis.edu
http://cesandiego.ucdavis.edu/