A Brazilian study evaluated the effects of top pruning on orange trees located on the edges of an orchard as part of an HLB management strategy. The pruning was an attempt to attract the HLB-spreading psyllid from external areas to the orchard edges and control it, reducing its dispersion into the orchard.
Fundecitrus and Embrapa Cassava and Fruits conducted the research, and the São Paulo Research Foundation (FAPESP) and Fundecitrus financed it. An article about the study, Topping sweet orange trees as Diaphorina citri bait on the farm edge for huanglongbing management: Opportunities and limitations, was published in Scientia Horticulturae.
Pruning stimulates the emergence of shoots at the top of the plants, which is the Asian citrus psyllid’s main source of food and place for reproduction and development.
The study compared, over three harvests, plots of sweet orange trees of different varieties pruned only at the top, at around 4 meters in height, and others that were not pruned. At the edges, it was observed that trees with top pruning every 30 to 45 days on alternate rows showed twice as much sprouting on average as unpruned trees. In some varieties, the psyllid population was 70% higher, and the cumulative incidence of HLB was 90% higher when compared to plants that were not pruned.
However, due to failures in controlling the psyllid, the technique was unable to reduce the dispersion of the vector and the spread of the disease into the interior of the plot. The interior of the plot was not pruned during the study.
Embrapa researcher and article co-author Eduardo Girardi assessed the results of the study as important but drew attention to the need for rigor in controlling the insect. “It was evident in some varieties, such as Hamlin, that top pruning stimulated greater sprouting, and this is capable of attracting more psyllids,” Girardi said. “However, at the same time, this practice on the edges increases the risk of a high insect population if there is not very good control using effective insecticides at the correct rotation and frequency.”
The study also noted that frequent top pruning reduced plant production and, therefore, this practice on borders should not be recommended without great care with vector management. “If insect management fails, the insect infestation in plants with intense sprouting will be greater and, consequently, the risk of increasing the disease will be very high,” said Fundecitrus post-doctoral fellow and study co-author Deived Cavalho.
Also participating in the study were researchers Camilla de Andrade Pacheco, Isabela Vescove Primiano, Daniela Kharfan, Alécio Souza Moreira, Francisco Ferraz Laranjeira and Renato Beozzo Bassanezi.
Source: Fundecitrus
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