Effect of pruning time and severity on the growth of 'Chandler' and 'Lara' trees in Tasmania, Australia

To improve the growth of young, non-bearing walnut trees, pruning trials were conducted over three years using ‘Lara’ and ‘Chandler’ cultivars in a Juglans regia orchard located in Tasmania, Australia. Pruning was conducted at either dormancy or bud-swell in 2005-06 and 2006-07; all treatments were pruned during dormancy in 2007-08. In 2005-06, mean tree height and trunk circumference of dormant pruned ‘Lara’ trees increased by 38 cm and 3.3 cm, respectively; mean growth in bud-swell pruned trees was less at 30 cm (height) and 2.8 cm (circumference). Severe frosts and drought in 2006-07 reduced tree growth significantly. Pruning severity treatments were applied as a sub-plot to pruning time: ‘head’ pruning removed at least half the previous years’ shoot growth down to the growth of a circular solid stem, whereas ‘tip’ pruning removed only one quarter of the previous years shoot growth. Tip-pruned treatments included the removal of necked buds for 10 cm or 30 cm, below the apical bud, or non-removal of necked buds. In all years, the head-pruned trees had significantly greater shoot growth after pruning than tip pruned trees, resulting in no significant difference between treatments in tree height at the end of the growing year in 2005-06 and 2007-08. The removal of necked buds below the apical bud did not increase the growth of shoots in comparison to non-removal.