Efforts have been ramped up on the California-Mexico border to keep out a citrus pest known as the Asian citrus psyllid. The insect was trapped in Tijuana, less than two miles from the California border.

The psyllid can carry a bacterial disease called citrus greening, which renders the fruit bitter tasting and can kill citrus trees. Neither the disease nor the insect has been found in California.

Extensive surveys of citrus in California are being conducted by the California Department of Food and Agriculture near the border, and so far the pest has not been found on the California side.

The pest is originally from Asia. Previously, this pest had been known to be established in central Mexico, the Caribbean islands, and throughout Florida since its introduction there in 1998. More recent psyllid infestations include Texas since 2001, Hawaii in 2007 and coastal Louisiana in May 2008.

The psyllid is an efficient carrier of the bacterium that causes the disease called Huanglongbing (HLB), or citrus greening because the fruit does not color properly. Symptoms of HLB include yellow shoots and mottling and yellowing of leaves due to lack of the green pigment chlorophyll. Infected trees are stunted, sparsely foliated and may bloom off-season. In addition, there is twig dieback, leaf and fruit drop, production of small, lopsided, hard fruit, and small, dark aborted seeds. There is no cure for HLB, and diseased trees must be removed as quickly as possible to prevent spread of the disease.

In 2006, entomologist Beth Grafton-Cardwell of UC Riverside organized a team of researchers from the University of Florida and CDFA to develop a brochure, Web site and slide presentation to educate California citrus growers, the ornamental nursery industry and regulatory agency staff about Asian citrus psyllid and greening disease. The UC Exotic/Invasive Pests and Diseases Research Program funded the project.

"The Asian citrus psyllid was first discovered in Florida in 1998 and in three years, the psyllid was found statewide," Grafton-Cardwell said. "The psyllid infests certain ornamentals such as orange jasmine (Murray paniculata) and in Florida was spread by distribution of those plants by the big-box stores. This aspect is often overlooked by personnel only monitoring citrus and not closely related ornamentals. Also, fruit and plants that are trucked or flown into California from Mexico, Texas, Louisiana, Florida and Hawaii could carry the insect."

The HLB disease was found in 2005 in Florida and is spreading throughout the state. HLB is transmitted by the psyllid, by grafting infected plant material, and possibly by citrus seed. The disease could arrive in infected citrus trees, infected budwood or infected psyllids. The best prevention for the disease is to use only certified budwood in commercial and homeowner plantings, and for people to follow quarantine rules and not import citrus illegally.

CDFA and the Citrus Research Board have an HLB Task Force that has developed an action plan to respond to this pest and disease situation. If Asian citrus psyllid or HLB were to be found in California, an eradication program would go into effect.

For more information, visit the UC citrus entomology Web site at http://citrusent.uckac.edu