High altitudes limit the incidence of huanglongbing snd its vector, Diaphorina citri, in citrus orchards

Citrus fruit are important crops in many regions of the world and are valuable sources of carbohydrates, fibre and health-promoting compounds. Like other crops, production of these fruits is affected by a range of pests and pathogens that can affect the sustainable development of citriculture. The most devastating of these is huanglongbing (HLB), a bacterial disease caused by species of liberibacters, pathogens that are spread by insect vectors. Currently, there is no remedy for HLB, and management relies on the use of disease-free seedlings, the rouging of diseased trees, and pesticides to suppress populations of vectors. Our studies on HLB in Indonesia and Bhutan have shown that citrus grown at higher altitudes (above 1000-1200 m ASL) can remain free from the main vector of the disease, the psyllid Diaphorina citri, despite climatic conditions at these altitudes being favourable for the insect. Thus, sustainable production of citrus at these altitudes without the use of polluting agrochemicals may be possible. However, this would be dependent on the production and use of HLB-free propagation material, strict control on the movement of trees into these areas and the adoption of appropriate agronomic practices for the control of other pests and pathogens.