Foliage Canopy Development of ‘Mcintosh’ Apple Hedgerows in Relation to Mechanical Pruning, the Interception of Solar Radiation, and Fruiting1

Abstract

The percentage of solar radiation passing through the foliage canopy of ‘Mcintosh’ hedgerows, A) pruned annually by cutterbar and B) pruned by slotting saw, was measured continuously from pre-bloom until the completion of foliage growth in late July. Assuming the spur leaf canopy (Sp), emerges first and virtually completes growth before the shoot leaf canopy (Sh), emerges, the relative extent of Sp and Sh, and their respective interception of radiation is calculated at approximately 4-day intervals during the growing season. Even though A produced more total foliage and intercepted more total radiation, the spurs of B produced more flowers and more fruit. Spur leaf canopy B intercepted more solar radiation because of less shading by Sh. The maximum ratio Sh/Sp for adequate illumination of Sp is estimated to be about .8. The relative importance of sunlight on Sp and the time of interception of light during the growing season in relation to flower bud initiation and fruit development are discussed.