The U.S. citrus industry has been facing a serious threat from a disease that has spread from the East coast to the West Coast over the course of the last two decades, carried by a small insect that feeds on the leaves and stems of citrus trees.
Huanglongbing (HLB), better known as Yellow Dragon Disease or citrus greening disease, is spread by the Asian Citrus Psyllid (ACP). The insect, Diaphorina citri, is a hemipteran bug in the family Psyllidae, an important pest of citrus worldwide. Since first detected in Florida as early as 1995, the ACP has been confirmed in several states including Georgia, Louisiana, South Carolina, Alabama, Mississippi, Hawaii, Texas, Arizona, and California. ACP has also been confirmed in American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands.
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Citrus greening disease was first reported in Asia during the late 1800s and has already caused devastation in Asia, Africa, the Arabian Peninsula and Brazil. It is now infecting groves in the United States. Hit worst was the Florida citrus industry, which suffered the biggest threat in its history from the bacterial disease with no cure. By 2006 the disease had infected all 32 of the state’s citrus producing counties.
Economic losses attributable to HLB in Florida are estimated at greater than $1.7 billion, which translates to approximately a 16 percent reduction in grower revenues.
The disease has been confirmed in Texas and more recently California, resulting in citrus stock quarantines and concentrated chemical control efforts to reduce populations of the psyllid that spreads the disease.
While chemical agents have proven partially effective, concerns over use of pesticides and their effectiveness have caused officials to seek better and sustainable alternatives to achieve better population control.
Problems associated with spread of ACP
ACP can cause economic damage to citrus in groves and nurseries by direct feeding. Both adults and nymphs feed on young foliage, depleting the sap and causing galling or curling of leaves. High populations feeding on a citrus shoot can kill the growing tip.
ACP's primary threat to citrus, however, is not as a direct plant pest, but as an efficient vector of the bacterial pathogen that causes citrus greening, Huanglongbing, considered to be one of the most serious citrus diseases in the world. HLB is a bacterial disease, caused by strains of the bacterial pathogen Candidatus Liberibacter asiaticus that attacks the vascular system of host plants. HLB greatly reduces production, destroys the economic value of the fruit, and can kill trees.
Once infected, there is no cure for a tree with HLB. In areas of the world where the disease is endemic, citrus trees decline and die within a few years and may never produce usable fruit.
Proposed issuance of permits
Biological control may help. The Animal and Plant Health Inspection Service (APHIS) is proposing to issue permits for the field release of a parasitic wasp, Diaphorencyrtus aligarhensis, to reduce the severity of infestations of ACP in the United States and retard the spread of HLB. While the proposed release is expected to directly involve ACP areas in California initially, it is not limited to one geographic area in the plan and could be expanded.
APHIS released a statement last week advising the public that a draft environmental assessment has been prepared relative to the proposed release of Diaphorencyrtus aligarhensis for the biological control of the Asian citrus psyllid in the contiguous United States. They are making this environmental assessment available to the public for review and comment.
A preliminary review and comment period relating to the proposed biological control method was made available by APHIS earlier this year (September, 2014) and provided the public with the opportunity to comment on a proposed plan. A total of 16 comments were properly submitted and were evaluated by USDA-APHIS who subsequently investigated and initiated additional investigations relative to those comments.
The final draft environmental assessment has been prepared by APHIS and is available for review and additional comment. To review the final environmental assessment and for information on how to comment, follow this link.