Response of Two Novel Peach Tree Growth Habits to In-row Tree Spacing, Training System, and Pruning: Effect on Growth and Pruning

Abstract

Novel peach [ Prunus persica(L.) Batsch.] tree growth habits, such as the pillar (P) (also called columnar) and upright (UP), offer unique opportunities to develop high-density peach production systems similar to that for apple. This study was initiated to examine the performance of a novel P and UP growth habit compared to a standard (S) peach growth habit when planted at four different within-row spacings and trained to a multiple leader (ML) or central leader (CL) system. The effect of summer pruning (SP) was examined over five growing seasons. In the final year of the study, canopy height was significantly reduced on one half of the trees in each growth habit x spacing x training system plot to determine the response to radical tree height adjustment for bearing upright and columnar peach growth habits. The three growth habits differed in trunk cross-sectional area (TCSA) after seven growing seasons with P trees being smallest and UP habit trees the largest. Close in-row spacing (1.5 and 2.0 m) reduced TCSA compared to wider spacing (4.0 and 6.0 m). There was a significant interaction between spacing and growth habit for TCSA and for canopy width. At the close spacings growth was similar among the three growth habits, but at the wider spacings the TCSA and canopy width of UP and S trees were similar and much greater than P trees. SP annually from the second through the sixth leaf reduced TCSA and canopy width compared to non-SP trees. The year after SP was discontinued there were no significant differences in TCSA, canopy width, or terminal shoot growth between SP and non-SP trees. The effects of growth habit and spacing on terminal shoot growth were inconsistent and SP had little or no effect on mean terminal shoot length. P trees required less dormant pruning time and about 50% fewer pruning cuts per tree, but more time per individual pruning cut than UP or S trees. UP trees required about the same time to dormant prune in the seventh season as S trees, but required 35% fewer pruning cuts·cm ^-2TCSA than S trees. The effect of growth habit on pruning time is discussed. SP reduced the time required for dormant pruning between 28 and 50%, depending on year. SP was more effective in reducing dormant pruning time per tree for trees spaced at 6.0 m than trees spaced at 1.5 or 2.0 m within the row. Total pruning time (dormant with or without SP) per hectare was less for trees compared to UP or S trees when planted at the same in-row spacing. However, total pruning time was greater for a high-density P planting than a low-density planting of S growth habit trees. Our results indicate that P and UP growth habit peach trees are well suited to high-density planting systems at spacings of 1.5 to 2.0 m. However, the results do raise some questions about the horticultural benefit(s) of SP for these novel peach tree growth habits.