Why Are My Blackberry Canes Rotting with Grey Mould?

Grey mould (Botrytis cinerea) colonising blackberry cane tissue is a secondary infection that follows on from dead or injured cane wood — the fungus rarely attacks fully healthy living tissue but thrives on dead stubs, frost-killed cane tips, and old fruited canes left in place after harvest. The characteristic grey-brown fluffy growth on cane surfaces is most visible in damp conditions and in the dense interior of an unmanaged plant where air circulation is poor.

Where cane Botrytis originates

The most common source is old fruited canes left in place beyond their useful life. After the second-year canes (floricanes) have fruited, they begin to die naturally. If they are not removed promptly after harvest, the dying tissue becomes a colonisation site for Botrytis through autumn and winter. In a wet autumn, Botrytis growth on old canes can be dramatic — the dense grey coating is visible even from several feet away. This infected material produces billions of spores that persist in the plant environment and can affect fruit the following summer.

The post-harvest cane removal routine

Cut out all old fruited canes (those that have produced fruit in the current season) immediately after the last harvest. Cut to ground level. Remove all cut material from the site — do not leave it on the soil surface under the plant. This single action removes the vast majority of the Botrytis inoculum source in one operation and is the most effective cane Botrytis management step available.

Improving air circulation

Reduce the total number of canes in the plant to 6–8 well-spaced canes. A dense, congested plant with many canes creates poor airflow — the centre is persistently damp and still, ideal conditions for Botrytis. Spreading the remaining canes out across the full width of the support structure so that each has space around it reduces the disease pressure in subsequent seasons.