Control of Huanglongbing (HLB) Disease with Reference to Its Occurrence in Citrus Industry in the World

Huanglongbing (HLB) disease is one of the most severe diseases of citrus plantation all over the
world. HLB has destroyed an estimated 60 million citrus trees in Africa and Asia and more than 40
countries were infected by HLB in Africa, Asia and USA, The HLB pathogens are highly fastidious
phloem-inhabiting bacteria in the genus Candidatus liberibacter. The isolate from South Africa,
Candidatus liberibacter africanus is considered heat-sensitive and only found in Africa regions. The
isolate from Asia, Candidatus liberibacter asiaticus is the most severe strain and widespread. This
strain is heat-tolerant and can show the disease symptoms in humid, cool and hot temperature (up to
35°C). The isolate from America has been named Candidatus liberibacter americanus and it was
detected in Brazil and Florida. Current disease management strategies focus on vector control to
avoid infection within the farm or management of infected trees to eliminate source of inoculum. For
the Malaysia case, integrated pest management (IPM) is highly recommended to be adopted to
control the disease. The successes of individual or combined approaches depend upon on the
infestation level, knowledge and regulation. Basically, in the regions where disease incidence is low,
the most common practices are removal of symptomatic trees, intensive monitoring, pesticides
application and biological control of the vectors. Preventive and curative measures of infected trees
includes enhanced nutrition and plant hormone application by foliar sprays, regulating soil pH,
precision irrigation based on the needs of HLB-affected trees. In reality, effective disease control of
HLB is still difficult, especially in the area where the disease is widespread, vectors are well
established and the hosts are susceptible. In this article, possible HLB disease management
approaches are discussed.