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Managing nutrients for reducing bitter pit in ‘Honeycrisp’
Project Overview
Managing nutrient balance for reducing bitter pit in ‘Honeycrisp’ apple
Honeycrisp, a popular apple variety in New York, is highly susceptible to bitter pit – a physiological disorder related to calcium deficiency – causing significant economic losses to growers. This research helped to better understand the causes and develop proactive management strategies to prevent bitter pit.
Honeycrisp is a major apple variety grown in New York and the Northeast that nets growers a much higher wholesale price than most other varieties. However, Honeycrisp is highly susceptible to bitter pit, a physiological disorder related to calcium deficiency: growers lose an average of 15-25% of their Honeycrisp crop to bitter pit, and 60-80% of their crop in extreme cases, which causes significant economic loss to both growers and their rural communities. Growers try to combat bitter pit by spraying calcium on their trees, and applying lime and gypsum to soils, but these measures are not always effective. It’s clear that focusing solely on calcium is not sufficient to control bitter pit, and a more comprehensive management strategy is needed.
This project sought to better understand what causes bitter pit in Honeycrisp apples, and to optimize the balance of calcium, potassium and other nutrients to improve growers’ profitability and wellbeing. We conducted both sand culture experiments and field trials on Honeycrisp and Gala apples over a wide range of nutrient conditions, then measured leaf and fruit nutrient status, fruit size, quality and yield. To understand how potassium, calcium and other nutrients are taken up in leaves and fruit in Honeycrisp trees, we monitored trees throughout fruit development, assessing both nutrient status of fruit and functioning of xylem vessels, which transport water and minerals in plants. We also surveyed commercial Honeycrisp orchards in western New York to assess how bitter pit risk is related to the potassium/calcium ratio in fruit peel sap at two months after bloom, when the fruitlets were about 55 to 60 grams.
The Impacts
We found that, due to poor function of the fruit xylem vessels, Honeycrisp fruits only take up half the calcium taken into Gala fruits, but they have much higher potassium levels in their peels. The imbalance of calcium to potassium underlies the high susceptibility to bitter pit in Honeycrisp. To ensure good fruit growth while reducing bitter pit risk, the optimal leaf and fruit potassium levels for Honeycrisp are 1.0-1.3% and 0.5-0.7%, respectively – lower than the 1.3-1.8% and 0.7-0.9% recommended for Gala and other varieties. We also found that the ratio of potassium to calcium in fruit peel sap at two months post-bloom offers a good assessment of fruit nutrient status and bitter pit risk. The diagnosis of fruit nutrient status and prediction of bitter pit risk in Honeycrisp mid-season afforded by peel sap analysis enables farmers to implement mitigation practices to reduce bitter pit risk at harvest and during storage. This service has been offered to Honeycrisp growers throughout New York as a tool for managing Honeycrisp bitter pit since 2021.
The management strategies developed through this project have helped to sustain the productivity and profitability of the New York apple industry, which benefits rural communities in apple-producing regions of the state. Consumers in New York state and across the country have also benefited from better supplies of high-quality Honeycrisp apples.
Principal Investigator
Project Details
- Funding Source: Hatch
- Statement Year: 2022
- Status: Completed Project
- Topics: Apples, nutrient management, disease management