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United States Department of Agriculture

Agricultural Research Service

Title: Huanglongbing: The dragon arrives in the USA

item Gottwald, Timothy
item Dixon, W. - FDACS
item Parnell, Stephen
item Riley, T. - USDA, APHIS

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: July 14, 2006
Publication Date: July 22, 2006
Citation: Gottwald, T.R., Dixon, W., Parnell, S.R., Riley, T. 2006. Huanglongbing: The dragon arrives in the USA. Huanglongbing-greening International Workshop, July 14-21, Ribeiro Preto, Brazil. P13-14.

Technical Abstract: Huanglongbing (HLB) was first discovered in an exotic fruit planting in Florida City, in south Florida on August 23, 2005 by Dr. Susan Halbert, Florida Department of Consumer Services, Division of Plant Industry (FDACS/DPI) during a targeted survey for new exotic citrus pests. In late August, FDACS/ DPI confirmed the presence of HLB via PCR assays and has been determined since to be endemic in Florida. On September 2, the infection by Candidatus Liberibacter asiaticus (CLa) was confirmed by USDA, APHIS in Beltsville, Maryland. Within a few days, additional suspect samples were collected and confirmed form the Pinecrest residential area of south Miami about 29.8 km (18 mi) to the northeast of the initial discovery. USDA, APHIS immediately deployed an emergency strike team to perform a delimiting survey. The survey was three-fold: First, the survey consisted of a circular transects at 8-km (5-mi) intervals around the initial infection, and samples were taken every 1.6 km (1 mi) of the transect perimeter. If the disease was discovered in the initial transect, then survey crews performed a second transect, etc. until no more HLB discoveries were made. At that time, radial transects were arrayed extending back toward the center to determine the edge of infection. Unfortunately the disease was soon discovered to have already spread beyond several radii and the leading edge to the disease was not discovered. This necessitated a second survey strategy during which east-west transects were used at 8-km (5-mi) intervals extending northward from the south Florida infection along the central Florida coast. HLB infection was found to extend as far north as St. Lucie County, over 240 km (150 miles) from the point of discovery. Simultaneously, it was suggested that survey inspectors also examine the southern and eastern edges of the nearest commercial plantings. These also revealed multiple commercial plantings infected. In October and December, 2005, the USDA/APHIS and the FDACS/DPI convened a science panel of HLB experts to assess the distribution and recommend a course of action. After examining the survey results and reviewing prior knowledge of HLB, its biology and vector transmission, the science panel opined that the disease was already too widespread to attempt eradication and had become endemic to Florida. The science panel recommended continuation of the survey to delimit the infection and the severity of disease within infected areas. Subsequent surveys have shown that the disease has already spread to 12 counties across southern Florida. The science panel also recommended a review of possible disease mitigation/control options including rouging, biocontrol, and insect vector control and immediate nursery certification program changes. The University of Florida and USDA/ ARS presently are testing various disease mitigation/control options in commercial plantings in Florida. In addition, the USDA/APHIS, FDACS/DPI and commercial citrus industries have undertaken the development of a Citrus Health Response Plan (CHRP) to develop national guidelines and protocols for commercial citrus nurseries, producers, harvesters, and packinghouses to best contain HLB as well as citrus canker, and mitigate disease spread. An additional delimiting survey is now planned. This will be a combined HLB/Citrus Canker statewide commercial planting survey targeted toward the more susceptible plantations. To accomplish this survey all citrus plantings within the state of Florida are ranked by susceptibility to both HLB and citrus canker relative to their respective citrus species/cultivar type. Manpower and fiscal resources are assessed to determine how much area can be surveyed within a 90-day timeframe. Estimates indicate that approximately 15% (38,243 ha = 94,500 acres) of the total commercial area 255 ha (630,000 acres) can be surveyed within this timeframe. A software routine was developed to stochastically select approximately 15% of the commercial citrus area that resides within each township (an area consisting of 93.2 km2 = 36 mi2 as defined by the US Geological Service). The routine calculates a combined HLB/Citrus Canker susceptibility index related to each commercial block and then randomly selects blocks within each township with a bias toward those with higher susceptibility. The biasing routine can equally weight the two diseases or skew the bias toward one or the other. In this case, it was determined to skew the bias toward HLB by a ratio of 2:1 over citrus canker. This combined 15% sampling protocol will commence in July 2006. Depending on its outcome, a second sampling phase may be undertaken. This sampling protocol can also be used in other citrus-producing states such as Texas, California, and Arizona and serve as an early detection survey for these two diseases.

Last Modified: 4/21/2014
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