Mouldy core is an internal dry rot of certain apple varieties. External symptoms are rare but fruit may colour and fall prematurely. The problem is characterised by the growth of fungus mycelium within the apple core, initially without invading the apple flesh. The fungi may invade the flesh leading to a slow, dry rot confined to the apple centre. The core rot may also continue to develop in store and may then appear at the cheek, eye or stalk end of the fruit. This is often true where the core rot is caused by Fusarium spp.
Some apple varieties, especially Bramley, can be affected by a wet core rot. This appears after harvest or post storage, usually as a soft, internal rot that eventually rots the whole fruit. Wet core rots are caused by a range of fungi including Fusarium, Mucor and Penicillium. Wet core rots generally arise from fungi that enter the core when the fruit is drenched post-harvest in anti scald agents.