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Mechanical harvesting of sweet chestnut pruning residues: proposal of sustainable method promoting the establishment of Torymus sinensis

M. Pagano, M. Fedrizzi, M. Guerrieri, R. Tomasone, C. Cedrola, G. Sperandio, A. Acampora, D. Pochi
Acta horticulturae 2018 v. no.1220 pp. 95-102
Castanea, Dryocosmus kuriphilus, Torymus, abortion (plants), adults, biological control, burning, cleaning, galls, larvae, mechanical harvesting, natural enemies, orchards, parasitic wasps, pruning, shoots, shredding, spring, Italy
Severe infestations of the Asian chestnut gall wasp (ACGW) are affecting sweet chestnut orchards across Italy, drastically impacting nut yield. The pest causes bud alteration and induces gall formation, preventing normal shoot growth and causing flower abortion. ACGW management in infested orchards is difficult, chemical suppression is ineffective against larvae within the gall. Control through cultural practices involves pruning out galled shoots, eliminating the residue from the orchard by burning. A feasible biological control strategy utilizes the parasitic wasp Torymus sinensis. The parasitic larvae feed on the gall wasp developing in green galls, but adults emerge from the woody galls the following spring. To promote the establishment of this natural enemy in chestnut orchards, the pruning residue with galls should be kept on the field and not destroyed. This paper describes an innovative agro-mechanical practice, used for cleaning up the orchard floor, removing prunings and preparing the field for mechanical harvesting of chestnuts. The trials, carried out in the “Monti Cimini” area in the Province of Viterbo, involved the use of an innovative tractor-pulled, one-process mechanical system for picking-up, shredding and accumulating the pruned material, simultaneously. In the field tests the machine shredded the residue effectively, accumulating the fragments in the trailed container, achieving an average gross operative capacity of 1.19 ha h-1 and extracting 3.48 t h-1 of residues from the orchard aisles. Once the container was full, the shredded prunings were dumped in several areas to distribute the piles in the orchard. The analysis of shredded residue samples, collected from the piles, showed that the impact of the mechanical process did not compromise gall integrity, essential for the development of the parasitic wasp.