Orchard training systems influence early canopy development and light microclimate within apple tree canopies

Delicious and McIntosh apple trees were trained to five orchard systems: central leader (two spacings), slender spindle, van Roechoudt trellis, and vertical axe. Radiation measurements were taken at the bottom of the canopy throughout the season or at various heights within the canopy after the growth of the canopy was completed. Early in the life of the plantings slender spindle and vertical axe trees of each cultivar had the highest yields expressed on a per hectare basis. By the fifth year of the planting, McIntosh trees trained to the slender spindle and the narrow central leader spacing were producing similar amounts of fruit. Light levels at the bottom of the canopy for some orchard systems were at or below 30% of full sun as early as 25 d after petal fall. Orchard system affected total leaf area and the number of spurs per tree in both 1989 and 1990. The low light levels at the bottom of the canopy reported in this study suggest that attention to pruning and training in the early stages of the orch...