Impact of Crop Load on Fruit Size, Color and Return Bloom of ‘Honeycrisp’ Apple across Four US Locations

Abstract

Effective crop load management programs are critical to maximize apple orchard profitability. A series of coordinated experiments were conducted at four locations in the United States (Michigan, North Carolina, New York, and Washington). The studies aimed to determine the relationship between crop load and yield, fruit size, color, and return bloom of ‘Honeycrisp’. Mature and uniform ‘Honeycrisp’ apple trees grafted on ‘M.9’ rootstock were selected at each location. Crop load, expressed as fruits/cm2 trunk cross-sectional area (TCSA), was used to standardize trees and provide a physiological context for interpreting fruit size and yield efficiency. Fruit size, independent of crop load, among the four locations was positively correlated to growing degree hours from green tip to full bloom and average daytime temperature from 6 weeks after bloom until harvest. The percentage of marketable red blush area and return bloom were negatively correlated with the final crop load at all locations and years. Fruit red color, independent of crop load, among the four locations was positively correlated to growing degree hours from green tip to full bloom, and average solar radiation the week before harvest negatively correlated to average daytime temperature the week before harvest. Return bloom the following year was also negatively correlated to crop load. Return bloom, independent of crop load, among the four locations was positively correlated to growing degree hours from full bloom to 6 weeks after full bloom and negatively correlated to average of radiation from green tip to full bloom. The market-preferred fruit size for ‘Honeycrisp’ (200–250 g) was achieved with different crop loads depending on the region and weather conditions (between 4.4 and 13 fruits/cm2). However, a general range of 4.5 to 6 fruits/cm2 TCSA is recommended to balance size, color, and return bloom.