Prebloom foliar boron, zinc, and urea applications enhance cropping of some 'Empire' and 'McIntosh' apple orchards in New York

Abstract

This study was initiated to determine if prebloom sprays of B, Zn, and urea would enhance cropping of apple (Malus xdomestica Borkh.) after cold injury, hypothesizing that they may accelerate recovery of damaged vascular tissue. The following foliar nutrient treatments were applied prebloom to 'McIntosh' and 'Empire' trees at two sites in 1994 and 1995:1) control;2) B (22.8 mM) at half-inch-green; 3) Zn-EDTA (0.75 mM) at half-inch-green; 4) B and Zn-EDTA at half-inch-green; 5) B, Zn-EDTA, and urea (59.4 mM) at half-inch-green; 6) B and Zn-EDTA at half-inch-green, followed by B, Zn-EDTA, and urea at pink. In 1994, following a very severe winter that caused visible damage to vascular tissue, 'Empire' at both sites cropped more heavily following all treatments that included both B and Zn; such treatments increased cropload by an average of 22% and 35% at the two test sites. Despite a mild winter preceding the 1995 season, prebloom nutrient treatments again increased cropping of 'Empire'. In 1996, treatments included a control and a single foliar treatment (B + Zn-EDTA at half-inch-green followed by B, Zn-EDTA, and urea at pink) on 'McIntosh' and 'Empire' at seven orchard sites. Treatment enhanced cropping in 'McIntosh' at three of the seven sites, but there was no effect on 'Empire'. Factors influencing differences in response were not apparent from this study, although a complex of factors may be involved. Data for all years indicated that prebloom nutrients did not enhance spur leaf development or fruit set; such treatments probably enhance cropping by increasing retention of flower buds that would otherwise abscise before anthesis. Where cropping was increased, mean fruit weight was not reduced at P ≤ 0.05 but fruit weight was significantly less at P ≤ 0.10 in 1995. Chemical names used: boron (Solubor, disodium octaborate tetrahydrate); zinc (Zn-EDTA, zinc chelate).