Grey mould (Botrytis)

Botrytis cinerea Pers., 1794 (sexual stage Botryotinia fuckeliana (de Bary) Whetzel) · formerly or also: Botryotinia fuckeliana

gray mold / Botrytis bunch rot · English, Americas
podredumbre gris / moho gris · Spanish, Spain and Latin America
pourriture grise · French, France
mofo-cinzento · Portuguese, Brazil and Portugal
Grauschimmel · German, Central Europe

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Grey mould is a fluffy grey fungus that rots strawberries, grapes, tomatoes, flowers and hundreds of other crops in cool, humid conditions, both in the field and after harvest. It often infects flowers and wounds and waits unseen until fruit ripen. It is one of the most important pathogens in the world and one of the quickest to resist fungicides.

Raspberries rotting with grey mould. Photo: Schlaghecken Josef, CC BY 4.0, via Wikimedia Commons.

Type: Fungal disease · Fungus (ascomycete)
Classification: Fungi › Leotiomycetes › Helotiales › Sclerotiniaceae
Main crops: Strawberry, Grape, Tomato, Cucumber, Lettuce, Blueberry, Ornamentals
Found in: Europe, Americas, Asia, Africa and the Middle East, Oceania
Chemical groups: FRAC 9, FRAC 12, FRAC 17, FRAC 7, FRAC 2, FRAC M04, FRAC BM02 (mode-of-action groups, not products)
Last reviewed: 2026-10-19

What causes grey mould?

Grey mould is caused by Botrytis cinerea Pers., 1794 (sexual stage Botryotinia fuckeliana (de Bary) Whetzel), a fungus (ascomycete) (order Helotiales, family Sclerotiniaceae).

Older or alternative scientific names: Botryotinia fuckeliana.

Where it occurs

Found worldwide, in every climate where crops are grown, and especially important in greenhouses and in humid, cool growing seasons.

Region	Status
Europe	Widespread; major in vineyards, berries and greenhouses
Americas	Widespread
Asia	Widespread; major in protected vegetables
Africa and the Middle East	Widespread, especially in protected crops and export flowers
Oceania	Widespread

Symptoms and identification of grey mould

Grey mould (Botrytis cinerea) on a plant. Photo: Flowersabc, CC BY-SA 2.0, via Wikimedia Commons.

The organism

The fungus produces dense, grey to grey-brown, velvety or fluffy masses of spores on tree-like stalks (the name means 'grape-like', after the spore clusters). It forms hard black sclerotia on dead tissue, which survive in soil and debris.

Signs in the crop, stage by stage

Crop stage	What you see
Flowering	Brown, rotting petals and flowers; infection of stamens and flower parts that later spreads into fruit; 'ghost spots' (pale rings) on tomato fruit where spores germinated without causing rot.
Fruit development and ripening	Soft, light brown rot spreading from the calyx or a wound, soon covered by grey fuzzy spores; in grapes, rotting berries that spread through tight bunches; stem cankers on greenhouse tomato.
Harvest and storage	Rot develops on fruit and flowers in transit and storage, spreading by contact (nesting).

Disease cycle of grey mould

Life cycle of Grey mould (Botrytis) — diagram drawn by Laisha from the stages below. Durations depend on temperature.

Spores from rotting tissue, debris and sclerotia are carried by air currents and water splash. They germinate on wet surfaces and invade mainly through flowers, wounds and senescent tissue. Infection of flowers can stay latent until fruit ripen and sugars rise, so rot appears later, often after harvest.

Stage	Duration	Notes
Survival	Months to years	Sclerotia and mycelium in debris.
Spore release	Continuous in humid weather	Airborne conidia.
Infection of flowers and wounds	Needs several hours of wetness or humidity above about 90%	May remain latent.
Rot and sporulation	A few days in favourable conditions	New spores spread to other fruit.

Temperature

Grows from about 0 °C (it can rot fruit in cold storage) to about 30 °C, with an optimum near 15-25 °C; long periods of high humidity and free water drive infection.

Generations

Many cycles through the season wherever humid conditions and susceptible tissue occur.

Conditions that favour it

Cool, humid or rainy weather during flowering and ripening, dense canopies, tight grape bunches, wounds from hail, insects or handling, excessive nitrogen, condensation in greenhouses and storage at high humidity.

Economic threshold level (ETL)

There is no numeric economic threshold based on disease counts; programmes are preventive, timed to flowering and pre-harvest periods, and adjusted by weather-based risk models in some crops (for example strawberry and grape).

Thresholds are local. They depend on crop price, control cost, variety and natural-enemy activity, so use the figure your local extension service publishes where one exists.

Damage and yield loss from grey mould

Pre- and post-harvest losses of 20-50% occur in strawberries, grapes and other soft fruit in wet seasons; in grapes, rot also lowers wine quality. Global losses are estimated in the billions of US dollars a year.

Monitoring

Inspect flowers and fruit near the canopy interior twice a week in humid weather.
Use leaf-wetness and temperature risk models where available for strawberries and grapes.
Check stored and packed fruit regularly and remove rotting fruit immediately.
Monitor fungicide resistance in high-value crops where laboratories offer it.

How to control grey mould (integrated management)

Control works best as a sequence: prevent, monitor, then act only when a threshold or a risk forecast says so, using the least disruptive option that works.

Cultural control

Open the canopy (pruning, leaf removal around grape bunches, wider plant spacing) so flowers and fruit dry quickly.
Remove dead flowers, leaves and rotting fruit, and clean up debris.
Ventilate and heat greenhouses to avoid condensation; avoid overhead irrigation.
Harvest carefully, cool fruit quickly and store at low temperature.

Mechanical and physical control

Plastic rain covers or tunnels over strawberries and table grapes keep fruit dry.

Biological control

Microbial biocontrol agents such as strains of Bacillus, Trichoderma, Aureobasidium pullulans, Clonostachys rosea and Ulocladium are used in integrated programmes, mostly at flowering.

Host resistance

No crop is resistant; varieties with loose grape bunches, thicker berry skins or upright strawberry fruit trusses are less affected.

Chemical control of grey mould — by mode-of-action group only

Laisha names chemical options only by their resistance-committee mode-of-action group (IRAC for insects, mites and nematodes, FRAC for fungi, oomycetes and bacteria, HRAC for weeds), never by active ingredient or product. What is registered differs by country and changes over time; the label and your local plant-protection authority decide what may be used, on which crop, at what rate and with what pre-harvest interval.

Fungicides are applied mainly at flowering and before harvest, and the number of applications per group is limited because resistance develops quickly. Post-harvest treatments differ by country. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.

Scheme	Group	Mode of action	Notes
FRAC	9	Anilinopyrimidines (methionine biosynthesis)	Resistance documented.
FRAC	12	Phenylpyrroles (signal transduction)	Often mixed with Group 9.
FRAC	17	Hydroxyanilides (KRI, sterol biosynthesis class III)	Specific to Botrytis and relatives.
FRAC	7	Succinate dehydrogenase inhibitors (SDHI)	Resistance widespread in some regions.
FRAC	2	Dicarboximides	Resistance common.
FRAC	M04	Phthalimides (multi-site)	Protectant partner.
FRAC	BM02	Microbial biologicals with multiple modes of action	Biological partner.

Resistance management

Botrytis cinerea has developed resistance to almost every single-site group used against it, including FRAC Groups 1, 2, 7, 9, 11, 12 and 17, and multidrug-resistant strains occur in many strawberry and grape regions (FRAC Botrytis working group).
Use each group no more than once or twice a season, alternate groups, combine with multi-site and biological products, and rely on canopy and humidity management.

Look-alikes and how to tell them apart

Rhizopus and Mucor soft rots — Watery, leaking rot covered with coarse whitish hairs and black dots (sporangia), mostly after harvest in warm conditions.
Anthracnose of strawberry and pepper (Colletotrichum) — Firm, sunken, dark lesions with orange or salmon spore masses, not grey fuzz.
Sour rot of grapes — Vinegar smell and fruit flies in rotting bunches caused by yeasts and bacteria.

Host range

More than 1,000 plant species. Major crops include strawberry, grape, tomato, cucumber, pepper, lettuce, beans, berries, kiwifruit, stone fruit, onion and many cut flowers and ornamentals; it is a leading cause of post-harvest rot of fruit and flowers.

What is still uncertain

Resistance profiles change quickly and differ between farms.
Global loss estimates are approximate.

Grow guides for its host crops

How to grow the crop well is the first line of defence. Laisha's free grow guides cover each crop from sowing to harvest:

How to grow Strawberry How to grow Grape How to grow Tomato How to grow Cucumber How to grow Lettuce How to grow Blueberry

Not sure this is what you are seeing?Ask Laisha: describe the symptoms or send a photo, and get a reasoned first read with what to check next — for your crop, your stage and your region.Ask Laisha

Sources

Botrytis cinerea (grey mould-rot) datasheet — CABI Compendium. https://doi.org/10.1079/cabicompendium.9611
Botrytis cinerea (BOTRCI) — EPPO Global Database. https://gd.eppo.int/taxon/BOTRCI
Gray mold: Strawberry Pest Management Guidelines — UC IPM. https://ipm.ucanr.edu/agriculture/strawberry/gray-mold/
FRAC Botrytis working group recommendations — FRAC. https://www.frac.info/

Written by Laisha from the sources above, in its own words. This page is general reference, not a prescription: confirm identification locally and follow the label and your plant-protection authority.