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

This study was initiated to determine if prebloom sprays of B, Zn, and urea would enhance cropping of apple (Malus xdomestica Borkh.) after cold injur y, hypothesizing that they may accelerate recovery of damaged vascular tiss ue. The following foliar nutrient treatments were applied prebloom to 'McIn tosh) and 'Empire' trees at two sites in 1994 and 1995: 1) control; 2) B (2 2.8 mM) at half-inch-green; 3) Zn-EDTA (0.75 mM) at half-inch-green; 4) B a nd Zn-EDTA at half-inch-green; 5) B, Zn-EDTA, and urea (59.4 mM) at half-in ch-green; 6) B and Zn-EDTA at half-inch-green, followed by Il, 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 foll owing 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 mil d winter preceding the 1995 season, prebloom nutrient treatments again incr eased cropping of 'Empire', In 1996, treatments included a control and a si ngle foliar treatment (B + Zn-EDTA at half-inch-green followed by B, Zn-EDT A, and urea at pink) on 'McIntosh' and 'Empire' at seven orchard sites. Tre atment enhanced cropping in 'McIntosh' at three of the seven sites, but the re was no effect on 'Empire', Factors influencing differences in response w ere not apparent from this study, although a complex of factors may be invo lved, Data for all years indicated that prebloom nutrients did not enhance spur leaf development or fruit set; such treatments probably enhance croppi ng by increasing retention of flower buds that would otherwise abscise befo re anthesis. Where cropping was increased, mean fruit weight was not reduce d at P less than or equal to 0.05 but fruit weight was significantly less a t P less than or equal to 0.10 in 1995. Chemical names used: boron (Solubor , disodium octaborate tetrahydrate); zinc (Zn-EDTA, zinc chelate).