A study of the influence of pruning strategy effect on vibrational harvesting of apples

Fruit detachment efficiency (FDE) is one of the major factors defining the performance of mechanical harvesting. In addition to several important mechanical factors, mechanical harvesting would also be affected by tree physical characteristics. In this study, 'Jazz' apple variety in vertical-trellis-trained fruiting wall architecture with 6 in. (T6) and 9 in. (T9) of twig pruning treatments were used to analyze the effect of biophysical characteristics to FDE. Additionally, fruit quality and other harvest features in field test were also analyzed. A total of 2,082 fruits in around 270 limbs from 45 trees in the same block were marked with measurements of twig length and diameter before harvesting. Field harvest test was conducted using a Shake-and-Catch system developed at Washington State University with fixed vibrating frequency of 20 Hz and duration of 5 s. The harvest test results show that 90.8% ± 8.6% and 81.1% ± 6.9% of overall FDE can be achieved from treatment of T6 and T9, with a significant difference. FDE can reach up to 94% ∼ 97% when twigs were shorter than 10 cm, whereas it only remained around 57% ∼ 75% when twigs were longer than 23 cm. No significant difference of harvested fruit quality can be found between T6 and T9. While the fruit percentage of out of the catching device for T6 (1.6% ± 2.7%) was significantly lower than T9 (6.3% ± 8.3%), meaning T6 had a higher fruit collecting efficiency. This study indicates that pruning strategy certainly influenced the performance of a mechanical harvest system.