MECHANIZED MANAGEMENT OF PRUNING RESIDUES IN SWEET CHESTNUT ORCHARDS

Abstract

In Italy, Dryocosmus kuriphilus is a major insect pest of chestnut orchards causing
gall formation and significant yield losses. The use of the parasitoid wasp Torymus
sinensis is an effective biological control method that requires the appropriate
management of the pruning residues, to preserve the woody galls in which T.
sinensis adults overwinter. An innovative tractor-pulled combined mechanical
shredder was tested for treating the residues, once the pruning operations are
completed. The machine processes the residues in a single-step, picking-up the
prunings from the orchard floor, shredding them to appropriate size, and collecting
them into a rear container. The shredded residues may then be concentrated into a
few piles for the long-term field storage, until next spring. The aim of the study
was to evaluate the machinery’s operative performance, the quality of the shredded
biomass and the impact on gall integrity. In the field trials, the machinery
effectively shredded the residues achieving an average operative capacity of 1.19
ha∙h-1 and a work capacity of 1.79 t∙h-1. Moisture content, apparent bulk density,
and particle size distribution of the shredded biomass were determined. Over 95%
of wood chips were included in the 3.15-45 mm size range, making them suitable
for use in residential biomass furnaces. The calorific power of the chestnut residues
was similar to that reported for other hardwood species (18-20 MJ∙kg-1). Also, the
mechanical action of the shredder preserved at least two thirds of the winter galls,
safeguarding the parasitoid’s life cycle.