Mechanical vibration transmission and harvesting effectiveness is affected by the presence of branch suckers in olive trees

Trunk shakers are among the most widespread machines for mechanical harvesting in intensive olive orchards (300-500 trees ha−1). Harvesting effectiveness is an important issue for this sort of machine because, due to the heterogeneity of the tree canopy structure, vibration transmission is uneven and some branches vibrate poorly. The aim of the present work was to determine if the removal of internal suckers before harvesting could improve vibration transmission and harvesting effectiveness. 'Leccino' and 'Frantoio' trees trained to free vase and planted in an intensive olive orchard (400 trees ha−1) were used in experiments carried out in 2012 and 2013 in two different orchards. Triaxial accelerometers, placed on tree trunk and on the main branches, were used to measure vibration transmitted to the canopy by two custom-built orbital and multidirectional trunk shakers. On average, harvesting effectiveness increased significantly from 83.4% to 95.6% as a consequence of sucker removal. Maximum acceleration transmitted to the trunk and branches increased by 33.1% and 46.6% respectively after internal sucker removal. These results suggest that internal suckers reduce vibration transmission through the canopy, affecting harvesting effectiveness. Furthermore, the larger the fruit retention force per fruit mass was, the larger was the effect of sucker removal on harvesting effectiveness. These results suggests that sucker removal prior to harvesting is advisable to improve harvesting effectiveness in open vase trees harvested by trunk shakers, in particular when mechanical harvesting is carried out at an early stage of fruit ripening.