Symptoms
A grey-brown, fluffy coating of mycelium on flowers, fruit, leaves and shoots, preceded by watery, rotting spots. It attacks weakened and damaged tissue and develops rapidly in humidity and cool conditions and where air circulation is poor. Common on strawberries, begonias, peonies and roses. The coating is characteristically 'mousy' — fluffy and ashy grey, and when the infected tissue is knocked a visible cloud of spores (conidia) puffs up, which is a diagnostic feature of this disease. Infection usually starts in the weakest tissues: fading petals, wounds, hail marks or pest feeding damage, as well as pollen residue settled on the petals. Small, brown, watery spots appear on the flowers and quickly engulf the whole bloom ('flower blight'); from the infected flower the fungus often grows down into the shoot, causing it to constrict and die back. On soft fruit (strawberry, raspberry, grapes, tomato) a watery, browning rot develops, covered with a thick layer of grey, fluffy felt — the berry softens and 'dissolves'. On seedlings and cuttings Botrytis causes basal stem rot and the sudden collapse of plants. In older, dying mycelium and on plant debris hard, black, irregular lumps form — sclerotia (resting bodies), by which the pathogen overwinters in the soil and in plant debris. The disease also shows up after harvest, as a rapidly advancing storage rot of fruit and vegetables.
Treatment
Remove and destroy infected parts (do not compost), improve air movement and reduce humidity. Apply fungicides if needed. Early intervention is key — the disease spreads very quickly. Cut out and carry away from the growing area infected flowers, fruit and shoots as well as whole severely affected plants (ideally in the morning and on a dry day, when spores spread less); do not leave the debris in place or in the compost, as it is a source of further infections and sclerotia. Reduce watering and any operation that raises leaf wetness; in the greenhouse, polytunnel and in container growing, ventilate vigorously, lower the air humidity and space the plants more loosely. Disinfect cutting tools so as not to carry mycelium onto healthy tissue. Under heavy disease pressure, fungicides active against Botrytis are used, above all preventively and during flowering (the fungus enters mainly through the flowers), rather than only once a mass coating has appeared. Botrytis cinerea becomes resistant to single-site products very quickly, so it is essential to rotate products from different mode-of-action groups (FRAC classification) and not to exceed the recommended number of treatments. In storage, cool temperatures and low humidity only slow the progress of the rot — they do not replace removing damaged and partly rotten fruit before storing.
Prevention
Airy planting spacing (not too dense), watering at the base in the morning rather than the evening, avoiding wetting flowers and fruit, mulching strawberries, and removing plant debris. Ensure good air circulation around the plants: thinning cuts on shrubs and perennials, adequate spacing, and under cover constant ventilation and lowering of humidity — this is the most effective weapon, because Botrytis spores need a film of water on the tissue to germinate. Avoid wounds and damage (careful harvesting, protection against pests and frost), because the pathogen enters most easily through them; keep removing spent flowers, fallen petals and the first spoiling fruit before they become a base for spread. Fertilise in a balanced way — an excess of nitrogen produces lush, soft, watery tissue that is especially prone to infection, while an appropriate dose of potassium and calcium strengthens the cell walls. Mulch strawberries and other soft fruit so they do not touch the damp soil; harvest fruit grown under cover often and regularly. Choose healthy, disease-free planting material and — where possible — cultivars with a looser habit and lower susceptibility. Store fruit and vegetables cool, at low humidity and with good ventilation, using only healthy and undamaged specimens.
How to tell it apart from look-alikes
| Feature | Grey mould | Brown rot |
|---|---|---|
| Colour and type of coating | A uniform, fluffy, ashy-grey ('mousy') felt of mycelium | Cream to greyish-yellow sporulation cushions, without a uniform fluff |
| Arrangement of sporulation | A thick, even layer of mycelium on the infected tissue | Small sporodochia arranged in concentric rings on the fruit |
| Fate of the infected fruit | The fruit is watery, softens and 'dissolves' under the grey coating | The fruit browns, hardens and mummifies, often hanging on the tree |
| Favourable conditions | Cool temperatures and high humidity, weakened or wounded tissue | Warm, humid weather during flowering and ripening |
| Host range | Very broad: ornamental flowers, vegetables, soft fruit, cuttings | Mainly stone and pome fruit trees (+ blossom blight) |
Control — organic and chemical methods
Organic and biological methods
| Method | How it works | When to use |
|---|---|---|
| Sanitation — removing and destroying infected organs | Cut out and carry away from the growing area infected flowers, fruit, shoots and sclerotia; do not compost — it is a source of spores. | Continuously throughout the season, ideally in the morning on a dry day |
| Regulating humidity and air movement | Looser spacing, thinning cuts, ventilating covered structures and watering at the base in the morning — the fungus germinates only in moisture. | Preventively, stepped up in cool and humid periods |
| Balanced fertilisation (limiting nitrogen) | An excess of nitrogen produces soft, susceptible tissue; moderate nitrogen with potassium and calcium strengthens the cell walls. | According to the fertilisation plan during the growing season |
| Antagonistic biological products | Antagonistic microorganisms (Trichoderma, Bacillus, Clonostachys) act mainly preventively — as support, not as a rescue measure. | Preventively, before an expected infection, e.g. at flowering |
Chemical methods
| Method | How it works | When to use |
|---|---|---|
| Botryticide fungicides (single-site) with FRAC rotation | Anilinopyrimidines, SDHIs, phenylpyrroles, hydroxyanilides; Botrytis develops resistance quickly, so rotate the groups and do not overuse them. | Preventively and during flowering, under heavy disease pressure |
| Multi-site contact fungicide (protectant) | A multi-site contact product forms a protective barrier and reduces the risk of resistance within the spray programme. | As a protectant, before infection, in rotation with systemic products |
We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.
Sources
- Atlas of plant diseases
