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×domestica 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).