Low levels of calcium in the fruit are due to competition with shoots for calcium, which may be aggravated by weather conditions. Hot, dry weather in July or August tends to increase the incidence of bitter pit. Irregular irrigation may also increase bitter pit. Heavy dormant-season pruning, overthinning, and excessive nitrogen fertilizer promote bitter pit. Injury to trunks, such as winter freezes, interferes with calcium movement. Bitter pit occurs most severely in years of light crops.

'Northern Spy', 'Gravenstein', 'Grimes Golden', and 'Baldwin' are very susceptible to bitter pit. 'Golden Delicious' is moderately susceptible. 'Delicious' and 'Winesap' are fairly resistant.

1. Prune lightly by thinning out branches rather than by heading.
2. Head new shoot growth in summer on an overly vigorous tree. This may be done up until a month before harvest.
3. Apply five summer sprays about 1 month apart of calcium chloride or calcium nitrate at not more than 5 lb/100 gal. Add a surfactant to all sprays to reduce the possibility of burning. Higher rates will burn foliage and sometimes fruit. Sometimes calcium nitrate interferes with fruit color formation. Do not apply in hot weather. Spray must cover the fruits.
4. Where possible, use overtree sprinklers to cool trees in unusually hot weather.
5. Avoid excess nitrogen.
6. Use chemical thinning to avoid alternate-year bearing.
7. Avoid damaging trunks.
8. Maintain a constant soil moisture supply.
9. To avoid the condition in stored fruit, rapidly cool fruit after harvest then store at low temperatures, high humidity and under controlled atmosphere.