The Effect of Calcium Sprays and Fruit Thinning on Bitter Pit Incidence and Calcium Content in ‘Honeycrisp’ Apple

ABSTRACT

‘Honeycrisp’ is a recently released cultivar of apple (Malus x domestica) developed by the University of Minnesota, now in high demand by growers and consumers. This cultivar is susceptible to bitter pit, especially when the trees are young and the fruit load is low. The effects of calcium (Ca) sprays, fruit thinning, vegetative growth, fruit and leaf nutrient concentration on bitter pit incidence, and two sampling methods for nutrient analysis were studied. Bitter pit incidence was associated with several variables, including Ca and phosphorus (P) concentrations in leaves and fruits, magnesium (Mg) concentration in leaves, and yield parameters. Fruit Ca concentration and content for the growing season were modeled, which allowed the determinations of Ca levels associated with bitter pit incidence. Our data suggest that plug analysis was less sensitive than fruit-segment analysis for finding differences in Ca concentrations.

Keywords:

• fruit analysis
• mineral nutrition
• yield
• calcium nitrate
• Malus x domestica

ACKNOWLEDGMENTS

The authors thank James Luby, Cindy Tong, and Vince Fritz for reviewing this manuscript. This work was funded by the Minnesota Agricultural Experiment Station (Paper no. 041210139). Mention of a trademark name or proprietary product does not constitute a guarantee by the University of Minnesota.

Notes

^z Within sampling time, if significant differences exist, letters indicate mean separation in columns by Student-Newman-Keuls test, P ≤ 0.05.

^z Within sampling time, if significant differences exist, letters indicate mean separation in columns by Student-Newman-Keuls test, P ≤ 0.05.

^z Within sampling time, if significant differences exist, letters indicate mean separation in columns by Student-Newman-Keuls test, P ≤ 0.05.

^z If significant differences exist, letters indicate mean separation in columns by Student-Newman-Keuls test, P ≤ 0.05.