Saving California Citrus: Asian Citrus Psyllid and Huanglongbing Update

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The stakes are high in the fight to save California citrus from the threat of Asian citrus psyllid (ACP) and the disease it spreads, Huanglongbing (HLB) (also known as citrus greening). In Florida, more than 90 percent of commercial citrus trees are estimated to have HLB, and there has been a 70 percent decline in production, with an economic impact of $7.8 billion.

California growers and government have invested heavily in trying to contain the spread of the pest and disease. Because of this, and somewhat because of the varied geography of California compared to Florida, the pest has not spread as quickly here.

Nonetheless, there have now been about 30 detections of HLB-infected trees, centering in the Los Angeles neighborhoods of Hacienda Heights, San Gabriel, and, most recently, Cerritos (as of December 29, 2016). In these urban areas, the trees can be removed promptly, quarantines set up, and mandatory spray treatments initiated. Since there are more citrus trees in backyards than there are in commercial production, and since it is estimated that 60 percent of California homeowners have citrus trees in their yards, it is very important for the state and counties to stay vigilant in the detection and removal of infected trees.

The quarantine map right now looks like a patchwork of marked area throughout the central valley and central coast corridors. In November 2016 there were 11 notices of ACP finds, while in December there were nine more. These involve both urban and rural regions, from San Jose to Calexico, from Santa Nella to Nipomo to Clovis. In urban areas, the California Department of Food and Agriculture (CDFA) sends out notices that they will do mandatory ground treatment with Tempo SC Ultra (cyfluthrin) and Merit 2F or CoreTect (imidacloprid); the former for contact spray and the latter for soil application underneath host plants. In rural areas which have adopted the area-wide approach, they have an organic treatment protocol that growers are expected to follow in concert with other growers in the region affected.

The ACP detection map clearly shows that a large proportion of ACP finds occur along traffic corridors and around centers of citrus shipments such as juice plants. To try to address this, there are new regulations for mandatory tarping of citrus loads that move both within and outside of quarantine areas.

Grower meetings and trainings have been held in most citrus growing regions this fall and winter to train all involved parties on best management practices, such as cleaning field equipment, preventing spread of ACP, and packing house protocols.

As part of the ongoing efforts for better detection of HLB, CDFA has experimented with specially-trained dogs that can detect the disease in citrus trees prior to the development of symptoms. The dogs give an alert on certain trees and then follow-up testing is done to confirm the presence of HLB. Note that only the PCR test is currently approved for regulatory actions.

The California Citrus Pest & Disease Prevention Program’s Citrus Insider has further resources on best management practices and links to other important sites.