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African Greening Management
December 2021 / January 2022

African greening management in SA’s citrus orchards

SA Fruit Journal: December 2021 / January 2022

Managing greening disease caused by the bacterium “Candidatus Liberibacter africanus” (CLaf) in orchards, is a challenge. And to combat it successfully requires a fully integrated management approach, as well as an area/regional approach. By MC Pretorius and James Warrington

Historically, for more than 40 years greening disease has been successfully managed in Nelspruit’s Karino area in the Mpumalanga Lowveld. At a height of between 600 – 850m above sea level, a sub-tropical climate, mild winters and warm to very hot summers, the incidence of greening disease in this area is generally very high.

All citrus cultivars planted in the Nelspruit area are susceptible to greening. The biggest challenge occurs when lemons are grown in a greening-endemic area due to their characteristic year-round flush. Therefore, an area-wide decision was made by growers to refrain from planting lemons. Multiple flushes hamper effective vector control, resulting in the continuous spread of the bacterium, and creating additional inoculum sources that pose a threat to the region as a whole. Populations of the vector (Trioza erytreae) commonly known as psyllids, are endemic and occur in high numbers in orchards every season. If not managed well, this disease can eradicate citrus production as seen in the White River area, where citrus production was discontinued in the 1970s due to the incidence of greening.

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