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February / March 2024

HLB Safe System for citrus-tree production in nurseries

SA Fruit Journal: February / March 2024

Worldwide, Huanglongbing is the most feared disease in the citrus industry. By Paul Fourie and the CRI Biosecurity Advisory Committee

Huanglongbing (HLB), or Asian Citrus Greening, is caused by the bacterium Candidatus Liberibacter asiaticus, which is mostly spread by the insect vector Asian Citrus Psyllid (ACP), Diaphorina citri. As a well-publicised example, HLB has destroyed >80% of the US Florida citrus industry, where growers did not strictly follow the best-practice control measures.
There are no curative control measures, and the epidemic can only be effectively managed by a three-pronged approach: 1. Planting HLB-free trees, 2. Effective control of the insect vectors, and 3. Removal of infected trees. HLB control will fail if any of these three measures are not diligently implemented.

Preparing for the threat

Near SA, HLB and ACP have been reported in Mauritius, Reunion, and more recently in Kenya in East Africa. It is unlikely that HLB will be eradicated or contained in these countries, and it is expected that the disease will spread, following the natural range expansion of ACP along the east coast of Africa. Therefore, it is not a question of “if”, but rather “when” ACP and thereafter HLB will arrive in SA.

To prepare for the dreaded incursion, the CRI Biosecurity Advisory Committee has developed an HLB/ACP Action Plan for SA. The plan was adopted by an HLB Steering Committee on which DALRRD and all relevant stakeholders are represented. In short, it specifies the required surveillance and control measures, and associated actions, once HLB or ACP has been detected. These measures are specific for different incursion scenarios, viz. incursion of ACP only, HLB only, or ACP and HLB.

Following detection, a quarantine zone will be demarcated, surrounding the positive find site. Mandatory control measures will be ordered (insect vector control and/or removal of infected trees), and movement of citrus propagation material will be prohibited. Thus, landowners, including nurseries, inside quarantine zones will not be allowed to move any citrus vegetative material or trees.

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