HLB and HLB control measures reduced Florida orange juice production by several percent by 2008, and losses will likely increase, at least in the immediate future and possibly longer.
The two major parts of the Florida citrus industry are the larger juice processing sector and the more profitable, per acre, fresh market sector. The incompletely defined dynamic between citrus production and the processing plants is such that when plants operate below their most productive level, profits are threatened. If a plant closes, producers suffer reduced marketability of their oranges. Thus, declining production can induce a downward spiral.
In the Florida situation, HLB is entirely correlated with the presence of, and is presumed to require the participation of, CLas and its insect vector ACP.
In Brazil and in Florida, rigorous three-pronged programs have had a demonstrated saving effect in areas not yet severely affected by HLB. The programs rely on (i) production of citrus propagation materials in insect-proof facilities, which has been mandatory in Florida nursuries since January, 2008, (ii) strong reduction of the ACP population, and (iii) identification and removal of infected citrus trees, the principal reservoir of CLas. Although these programs have reduced the percentage of infected trees in some areas, the numbers of infected citrus trees in Florida as a whole continues to increase.
Increased use of insecticide sprays, as currently required for successful suppression of ACP populations, brings with it risks of ACP developing resistance to one or more of the most useful insecticides and of adverse affects on beneficial insects. More information on ACP behavior and HLB ecology and new approaches are needed to improve ACP suppression.
The identification and removal of CLas-infected citrus trees is currently dependent on scouting for visible HLB symptoms. The process is expensive, not sustainable for many orchards, and very likely would be greatly improved if infected but as yet asymptomatic trees could be identified.
The most powerful long-term HLB management tool likely will be citrus cultivars resistant to CLas and preferably to ACP as well. However, there is no clear path by conventional breeding to deliver a robust resistant citrus for many commercial species because these species lack known sources of resistance and a facile breeding system.
It is likely that the breeding systems for sweet orange and some other citrus can be greatly enhanced in the long run by capabilities derived from genome sequence analysis and other technologies.
Genetic engineering, in the form of transgenic citrus or citrus inoculated with a transgene-expressing virus vector, holds the greatest hope for generating citrus cultivars resistant to CLas and ACP.
New information on CLas, ACP and citrus, and the advances of modern biology and chemistry in general, suggest new research directions that may reveal new strategies for HLB mitigation.