Grey Mould Is Rotting My Strawberry Fruit

Strawberries developing a dense grey fuzzy mould — fluffy, dusty-looking, and covering whole areas of the fruit — have Botrytis cinerea, the grey mould fungus. This is the single most common disease problem on strawberries, particularly in the UK and northern Europe where cool, humid conditions during the fruiting season (May–July) create ideal conditions for Botrytis. It spreads rapidly from fruit to fruit and from infected tissue to healthy ripe fruit lying nearby. In a wet strawberry season, Botrytis can destroy a significant proportion of the crop within days of the fruit ripening.

How Botrytis spreads

Botrytis cinerea produces enormous quantities of grey dusty spores that spread through the air. Infection occurs when spores land on susceptible tissue — particularly damaged fruit, overripe fruit, or dead flower petals lying on the developing fruit. Cool temperatures (15–20°C) combined with high humidity and wet foliage create ideal germination conditions. The fungus can infect healthy-looking fruit through microscopic wounds or simply through contact with infected plant material or soil. Once a fruit is infected, the grey sporulation produces millions of new spores that infect neighbouring fruits within hours in humid conditions.

Straw mulch under the fruit

Placing a layer of clean barley or wheat straw under the developing fruit serves two purposes: it keeps fruit off damp soil (reducing direct soil-to-fruit infection) and it provides a clean dry surface that reduces humidity immediately around the ripening berries. Straw mulch is the traditional and most effective single physical control for grey mould. Apply it when flowers are present and the first fruits are forming, tucking it carefully under the leaves and around each plant. Do not use hay (which contains weed seeds) or wet straw.

Airflow and spacing

Dense plantings with poor air circulation create the humidity microclimate that Botrytis thrives in. Ensure adequate spacing between plants (at least 30–40 cm) and remove any dead leaves, spent flowers, or rotted fruit immediately — these are the primary infection sources. Picking every two days at peak fruiting removes ripe and overripe fruit before Botrytis has time to establish and sporulate. Never leave overripe or damaged fruit on the plant.

Chemical control

There are no fungicides approved for home garden use against Botrytis on strawberries in the UK as edible fruit. Cultural controls — straw, airflow, regular picking, prompt removal of infected material — are therefore the only tools available to home growers. In a very wet season these may not eliminate infection entirely but they significantly reduce losses compared to an unmanaged bed.