Why Are My Currants Going Mouldy Before Harvest?

Discovering that your currants are collapsing into a grey, fluffy mould while still on the bush — sometimes weeks before they would be ready to pick — is one of the most demoralising problems in the soft-fruit garden. The cause is almost always botrytis, also known as grey mould, caused by the fungus Botrytis cinerea. This ubiquitous pathogen is present in virtually every garden and needs only the right conditions to move from dormant background fungus to active destroyer of fruit trusses.

How botrytis infects currants

Botrytis cinerea infects through wounds, dead flowers, and senescent tissue. On currants, the most common infection routes are frost-damaged flowers in spring, and the dead calyx material at the base of each berry that can trap moisture against the skin. Once established in a single berry the fungus spreads to its neighbours in the truss, moving by direct contact and airborne spores. Warm, humid conditions — particularly wet weather during and after flowering — accelerate the cycle dramatically.

The role of air circulation

Dense, unpruned currant bushes with crowded centres trap moisture and create low-light, still-air conditions that botrytis exploits. Keeping the bush open by removing old and crossing wood allows damp air to escape and berry surfaces to dry after rain. Annual pruning is therefore not just about fruit production — it is one of the most important disease-prevention steps you can take. On established blackcurrant bushes, removing a third of the oldest, darkest stems each year creates the airflow that significantly reduces botrytis risk.

Wet weather at flowering and ripening

Two periods are especially critical: flowering in April to May, when frost-damaged or poorly set flowers leave dead material on the truss, and ripening in June to July, when skin integrity begins to break down on overripe berries. If the weather is persistently damp during either window, check trusses carefully and remove any berries already showing grey fuzz immediately — each infected fruit is a spore factory releasing millions of propagules into the surrounding air. Collect infected material in a closed bag and remove it from the garden rather than composting it.

Harvesting before the damage peaks

On a badly affected bush in a wet summer, the most practical response is to harvest as soon as the majority of berries in a truss have ripened, rather than waiting for complete uniformity. Slightly underripe red and white currants will continue to sweeten off the bush. Leaving trusses that are partly ripe to hang on in wet weather invites botrytis to move from the overripe end of the truss into the still-ripening berries. Picking promptly and refrigerating the fruit immediately is the most effective way to save the harvest once the fungus has appeared.

Reducing risk next season

After harvest, carry out a thorough clearance of any remaining diseased material, old trusses, and dying leaves. Rake up fallen berries from around the base of the bush — these often host overwintering botrytis. Apply a thick mulch of compost or bark to the base to suppress splashback of soil-borne spores onto low shoots. Consider thinning heavy truss clusters when the fruit is small — fewer berries per truss means less contact between them and better air movement inside each truss.