Most experience at East Malling has been obtained with Cox’s Orange Pippin apples. These should normally be treated with 9 kg 1000 litres-1 of flaked grade material although the rate may be increased to 13.5 kg 1000 litres-1 where the risk of bitter pit is high (Table 8).
These rates are believed to be generally safe although in some seasons fruit from certain orchards in East Anglia have been slightly damaged. Further studies related susceptibility to injury to differences in the structure of the fruit cuticle.
It is important to avoid over-dosing Cox apples with calcium chloride and to regard dipping or drenching in calcium as a last resort for improving their calcium status. The emphasis should be on the use of orchard sprays for supplementing calcium nutrition.
Cultivars of apple that have been treated safely with 9 kg 1000 litres-1 of calcium chloride include Spartan, Laxton’s Superb and Golden Delicious.
Bramley’s Seedling and Egremont Russett should not be treated with calcium chloride since severe lenticel injury may result. Calcium nitrate is not a permitted post-harvest additive and it is, in any case, more damaging than the chloride.
It is preferable that growers use proprietary formulations of calcium and follow the instructions provided on the label.