Eleven-year-old ‘Golden Delicious’/M. 26 apple (Malus domestica Borkh.) trees were left unthinned (483 fruit/tree), thinned to one fruit/spur (370 fruit/tree), or completely defruited. Leaf water potential, leaf stomatal conductance, and leaf water content were monitored during the growing season. From 3 weeks after thinning and continuing to harvest, trees with an average of 483 or 370 fruit had significantly lower leaf water potentials than defruited trees. Trees thinned to 370 fruit had consistently higher leaf water potentials than unthinned trees with 483 fruit. Leaves on unthinned or one fruit/spur trees had higher stomatal conductances than leaves on completely defruited trees, although these differences were detected later in the season than those for leaf water potentials. No treatment differences in leaf water content were observed. Defruited trees had higher specific leaf weights, longer shoot extension, and greater increases in trunk cross-sectional area than those not defruited. Fruit size was greatest on trees thinned to one fruit/spur.
Mature fruiting and defruited ‘McIntosh’/M.26 apple (Malus domestica Borkh.) trees were exposed to natural rainfall or to no rainfall with the use of under-canopy tent-like covers. With covers present, fruit diameter tended to be less and, on one occasion, soluble solids concentration and fruit firmness increased. Trunk growth was reduced more by fruit than by covers. Trunk growth of fruiting trees did not respond to covers, whereas trunk growth of defruited trees was reduced by covers. Fruit load and reduced soil water content did not affect terminal shoot length. In one experiment, specific leaf weight (SLW) was less for fruiting trees than for defruited trees. Fruiting increased foliar N, P, Ca, and Mg and decreased K concentration. On a leaf-area basis, K was again lower in cropping trees while other nutrients remained mostly unchanged. With tent covers, trees generally had less foliar N, P, and K based on either concentration or amount per unit of leaf area. Leaf water potential was lower for trees with fruit and tended to be lower for trees with tent covers. Leaf stomatal conductance was higher for fruiting trees than for defruited trees and higher for trees without tent covers than for trees with tent covers.