The citrus industry and various government agencies have made very significant investments in research on HLB and approaches to HLB mitigation. Results usable in effective HLB mitigation will probably be derived more rapidly from research projects if efforts are more unified than they are at present, on the national and international level, and there is more emphasis on strategic planning. When (or if) HLB no longer is a significant threat, an integrated research infrastructure would continue to serve the industry well.
The favorable conditions for citrus production in Florida have allowed the industry to grow to the point of having a $9.3 billion annual economic impact on the state. Throughout the Florida citrus industry’s history, this success has been tempered and defined by the adverse effects of the natural calamities of freezes, hurricanes and diseases, and, in more recent times, by urbanization, international competition, and shortage of water.
Due to the Great Freeze of 1894–1895, citrus production was abandoned in northern Florida and in other southeastern US states and has become concentrated in mid- and south-Florida. The Florida freezes of the 1960s provided an opening for the expansion of the Brazilian citrus production. Brazil now accounts for about 37 percent of the worldwide citrus production, whereas the United States’ share is about 17 percent. In 2004–2005, hurricanes were largely responsible for the reduction in sweet orange (38 percent) and grapefruit (69 percent) production compared to the year before. Urbanization has displaced citrus production from most of Florida’s coastal areas, leaving the majority of the production in the more freeze-prone inland areas. The seasonality of Florida rainfall means that virtually all Florida citrus is irrigated. A more subtle factor influencing the citrus industry is the interaction between production and processing, as indicated in Key Finding 4, above.
The first observations of diseased citrus corresponding to what is now recognized as HLB were in southern China in the late 19th century. In the mid-20th century, the Chinese researcher K.H. Lin provided a scientific description of HLB and demonstrated its infectious nature. At present, it is estimated that nearly 100 million trees in 40 countries are affected by HLB. In the 1960s–1980s, HLB devastated citrus production in the Philippines, Indonesia, Thailand, and South Africa. In March 2004, HLB was recognized for the first time in the Americas in São Paulo State, Brazil. Subsequently, nearly 3 million HLB-affected sweet orange trees were removed in Brazil. HLB was found in Florida in 2005. In North America, HLB now occurs in Cuba, Belize, Florida, Georgia, Lousiana, South Carolina, and Eastern Yucatan, Jalisco, and Nayarit, Mexico.
HLB enters a geographical region in an introduced psyllid vector or in infected live plant material. In the field, psyllid transmission (acquisition, retention through a latent period, then inoculation) is the primary mode of HLB spread. Thus, introduction and establishment of a vector species, which in Florida is ACP , always precedes establishment of HLB. In the principal mode of plant-to-plant transmission with an established psyllid population, older immatures acquire the bacteria, which circulate and propagate in the insects’ bodies while they complete