Botrytis Rot: How to Spot and Stop This Gray Mold on Plants?

It’s truly disheartening to see a beautiful plant, one you’ve nurtured with care, suddenly show signs of decay. Botrytis rot, that familiar fuzzy gray mold, can feel like a sudden betrayal, turning vibrant flowers and ripening fruit into a mushy, lifeless mess. This pervasive disease can strike a wide variety of plants, but armed with the right knowledge, you can fight back. This guide will help you understand what causes Botrytis rot, how to spot it early, and what you can do to stop it from ruining your garden.

What Is Botrytis Rot?

Botrytis rot, more commonly known as gray mold, is a widespread plant disease caused by the fungus Botrytis cinerea. This fungus is a necrotroph, meaning it kills its host’s cells and then feeds on the dead tissue.

It can infect over 1,400 different plant species, causing significant damage to flowers, fruits, stems, and leaves. The disease is infamous for its ability to ruin crops both in the field and after harvest, even in cold storage.

The fungus thrives in cool, damp environments. High humidity (above 90%) and prolonged periods of wetness on plant surfaces, often lasting more than six hours, create the perfect conditions for spores to germinate and infect a plant. It is particularly troublesome in greenhouses and during cool, rainy seasons from late fall to early spring.

What Plants Are Affected?

Botrytis cinerea is not a picky eater and affects a vast range of plants. Some of the most common hosts include:

• Grapes
• Strawberries
• Tomatoes
• Lettuce
• Ornamental flowers like roses, peonies, and geraniums

These plants are especially vulnerable because the fungus often targets soft, delicate tissues. It frequently infects blossoms, ripening fruit, and aging or wounded plant parts. For crops like strawberries and grapes, an infection that starts in the flower can remain dormant, only to emerge and rot the fruit as it ripens, which is a major cause of crop loss.

Causes of Botrytis Rot & How It Spreads

The fungus is almost always present in the environment, waiting for an opportunity. Understanding its triggers is the first step to control.

Common causes:

• Infected debris: The fungus survives on dead or decaying plant matter, like fallen leaves, old flowers, and unharvested fruit.
• Wounded tissue: Any injury to the plant, from pruning cuts to insect damage, creates an entry point for the fungus.
• Poor air circulation: Overcrowded plants trap humidity, creating a microclimate perfect for gray mold.
• High humidity & wetness: Cool, wet weather, overhead watering, and poor drainage are major contributing factors.

The spread of Botrytis rot is often hard to see at first. The fungus survives the winter in soil or dead plant matter as tough sclerotia or as dormant strands of mycelium. When the weather turns cool and moist, these structures wake up and produce spores that ride on wind and water.

Those tiny spores land on nearby plants, usually finding old petals, damaged spots, or aging flowers. From there, the fungus grows stronger, moves into healthy tissue, and creates the familiar gray mold that pumps out millions of new spores to start the whole process over again.

Disease cycle of gray mold (Botrytis rot) on strawberry, illustrating how spores spread via wind, moisture, and infected plant debris. (Source: New York State Agricultural Experiment Station)

Symptoms of Botrytis Rot 

• Water-soaked spots: Small, water-soaked or brownish spots often appear on petals, leaves, or fruit.
• Gray, fuzzy mold: The most obvious sign is a velvety, gray-to-brownish fuzzy growth on infected areas, which is a mass of fungal spores.
• Blighted blossoms: Flowers may turn brown, die, and become covered in mold.
• Soft rot on fruit: Infected fruit, like strawberries and grapes, develops a soft, brown rot and may collapse. In grapes, this can lead to a “slip skin” stage where the skin easily separates from the pulp.
• Stem cankers: On some plants, the infection can cause sunken lesions or cankers on the stems.

Symptoms of Botrytis cinerea on strawberry: A – mycelium on a dying flower; B – advanced blossom infection; C & D – fruit infection at different ripening stages (D shows infection from a petal); E & F – leaf browning and fruit decay.

How to Control Botrytis Rot?

Control Method	Key Strategies
Cultural Control	Improve air circulation through proper plant spacing and pruning; avoid overhead watering by using drip irrigation; water early in the day so foliage can dry.
Sanitation	Remove and destroy all infected plant parts, fallen leaves, and debris immediately; keep the garden or greenhouse clean to reduce sources of spores.
Resistant Varieties	Where possible, choose plant varieties that show some resistance to Botrytis, though complete resistance is rare.
Chemical & Biological Control	Apply fungicides preventatively during high-risk periods (cool, wet weather), rotating different types to prevent resistance; biological options like Serenade can also be used.

Conclusion

In the end, fighting Botrytis rot is about more than just quick fixes — it’s about smart tools and steady care. That’s where Planteyes shines: the app can detect plant diseases like Botrytis early from a simple photo, and you can even chat right in the app for tailored guidance that feels like talking to an expert who understands your garden. Download Planteyes today and give your plants the protection they deserve.

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