Small sunken pits develop on the surface of the fruit and the flesh beneath the pits is discoloured and dry. In severe cases, brown areas of tissue are scattered throughout the flesh of an infected apple and it takes on an unpleasant, bitter taste.
Symptoms can appear from when the fruits are about half developed until they are harvested or, often, do not develop until the fruits have been stored.
It is more common on young, vigorously-growing trees, especially those fed heavily with nitrogenous fertilisers; but it can also develop on fairly old trees, especially culinary cultivars with large fruit.
Some cultivars are particularly susceptible: 'Bramley's Seedling', 'Cox's Orange Pippin', 'Egremont Russet', 'Hamling's Seedling', 'Meridian', 'Merton Worcester', 'Newton Wonder' and 'Warner's King'.
Resistance: 'Jonagold' and 'Gala' appear unaffected by bitter pit.