Advice
RHS Help & Advice
Bitter pit in apples
Plants affected
Some cultivars are more susceptible than others; some are rarely affected.
Susceptible cultivars include: 'Newton Wonder', 'Warners King', 'Hamlings Seedling', 'Merton Worcester', 'Egremont Russet', 'Bramley's Seedling'.
Large fruits on young or vigorous trees are most prone to this disorder.
Symptoms
Sunken pits on the surface of the fruit appear late in the season and in storage. The flesh beneath the pits is discoloured.
Cause
This is not a disease, but a disorder caused by low levels of calcium in the fruit, due to irregular water supply to the tree and poor distribution of calcium within the tree. Excessive use of nitrogen, potassium and magnesium fertilisers can also cause or exacerbate the problem.
Treatment
This condition can be prevented by maintaining a uniform supply of water by watering throughout dry periods and using controlled-release fertilisers to provide a steady supply of nutrients.
Mulch to retain moisture in the soil around the tree.
Summer pruning of vigorous trees is also beneficial.
Foliar sprays of calcium nitrate fertiliser can be applied from mid-June to mid-September. Follow manufacturer’s advice on spraying intervals, but add a few drops of detergent to improve coverage. Spray in the evening to avoid ‘russeting’ (where apple skins develop rough, brownish patches). Never spray above 20°C (68°F). Use half-strength spray at more frequent intervals if russeting is problematic with scorch-prone cultivars such as ‘Bramley’s Seedling’.