Penicillium rot commonly occurs on all apple varieties at low levels either alone or as a secondary infection on other rots. The symptoms are similar on all varieties.
- This fungus invades fruit via wounds, bruises or cracks anywhere on the fruit surface or, on over-mature fruit, can invade via the lenticels.
- The rot is rarely seen in the orchard except occasionally on rotting fruit on the orchard floor.
- The fungus causes a pale green to dark brown circular soft rot which spreads rapidly over the fruit surface and into the flesh, forming a sharp interface between the healthy and rotted tissue, such that the rot can be scooped out.
- Sometimes after grading only the sound fruit with the rot cavity remains, the actual rotted tissue having dropped out.
- Open-eyed varieties such as Bramley may have Penicillium rot in the fruit centre, where the fungus has gained access via the drench solution during post-harvest treatment.
- Mature lesions are covered with brilliant white pustules which quickly turn blue, and give the rot its common name of blue mould.
- Penicillium rot can be spread by contact forming nests of soft disintegrating rots but can also rapidly colonise other rots such as brown rot and Phytophthora rot.