Combination of strategies to supply calcium and reduce bitter pit in 'Golden Delicious' apples

- The three main techniques to supply Ca to apples were tested to bitter pit control.
- Bitter pit was higher than 20% in two seasons and notably lower in other two seasons.
- Dip at post-harvest was more effective than pre-harvest treatments.
- The sprays mitigated bitter pit to a greater extent than Ca soil applications.
- No detectable advantage for starting spray programmes earlier than June.

Calcium (Ca) sprays and Ca applications to soil throughout the growing season or Ca solution dips at post-harvest are widespread practices to supply Ca and decrease bitter pit in apples. However, published results conflict, and there is no information about the effectiveness of combining all these treatments. In the present study, the following treatments were assessed during four growing seasons: early-season (April) Ca soil applications applied 4 times, mid-season (May) CaCl2 sprays applied 7 or 13 times, late-season (June) CaCl2 sprays applied 7 times, and the combination of late-season sprays and soil applications. In addition, post-harvest dips were evaluated in the latter two growing seasons. Notably high bitter pit incidences were monitored for the first and fourth year of study (>20%), while the second and third year were almost without incidence. Post-harvest dips mitigated bitter pit incidence to a greater extent than pre-harvest treatments, and the sprays mitigated bitter pit to a greater extent than Ca soil applications. The combination of sprays and soil applications did not improve the results relative to Ca sprays alone. No detectable advantage for starting spray programmes earlier than June was observed. Our results showed a trend towards reduced bitter pit with an increasing number of CaCl2 sprays, but this was not clearly an effect of maximizing fruit Ca. Finally, applying 13 CaCl2 sprays in combination with a Ca solution dip at post-harvest appeared to be the most effective practice for minimizing the risk of bitter pit development.