Treatment Plans
Treat Botrytis (gray mold)
Why does this gray coating attack your plants, and how can you stop it?
The problem
What you see is a very common fungus called Botrytis cinerea. It is everywhere in the environment as invisible spores, waiting for the right conditions to attack. It is not an aggressive predator; it is an opportunist. It mainly attacks already weakened tissue, as well as wounded or aging tissue, such as spent flowers and dead leaves. Once established, it produces enzymes that break down plant cells, creating wet, brown spots that quickly develop a characteristic grayish coating.
- The fungus thrives in high humidity above 90% and poor air circulation.
- Cool to moderate temperatures, between 17 and 23°C (about 63 to 73°F), are ideal for its rapid development.
- It spreads very quickly because the gray coating releases millions of new spores with the slightest touch or air current.
- Pruning wounds or leaves touching damp potting mix are perfect entry points.
Botrytis is an environmental problem before it is a plant problem. Correcting conditions matters more than treatment alone.
Its development cycle
The cycle can be explosive. Once a spore germinates on moist tissue, the first symptoms may appear within hours or days. The fungus survives winter as mycelium or sclerotia, small, hard black masses, in plant debris and soil, ready to reactivate as soon as conditions become favorable again.
| Stage | Estimated duration | Details |
|---|---|---|
| Dispersal | Constant | Spores (conidia) are everywhere, carried by air and water splashes. |
| Germination | A few hours | A spore lands on a moist surface, such as a leaf or petal, with humidity > 90%, and germinates. |
| Infection | 1–3 days | The fungus enters tissue, often through a tiny wound, and begins breaking it down. |
| Sporulation | 3–5 days | The characteristic gray coating appears. It consists of millions of new spores ready for release. |
This fast cycle explains why acting at the first signs is crucial to avoid widespread contamination.
What to do now
- Isolate the sick plant immediately. Botrytis is highly contagious and spreads on air currents.
- Use clean scissors or pruning shears. Disinfect the blades with 70% alcohol before and after every cut.
- Cut off all affected parts. Remove at least 2–3 cm (about 0.8–1.2 in) of healthy tissue below the infected area to make sure you eliminate all the fungus.
- Put cut plant debris in the trash, never in the compost, to avoid spreading spores.
- Increase air circulation around the plant. Move it to a better-ventilated spot or use a small fan on low speed for a few hours a day.
- Prepare a homemade fungicidal solution: mix 5 mL (about 1 measuring teaspoon) of baking soda and 2.5 mL (about half a measuring teaspoon) of black soap into 1 liter of water (about 1.06 US qt). Spray the whole plant, focusing on the areas where you made cuts.
- Reduce watering. Let the potting mix dry more between waterings to lower ambient humidity.
Prevention
- Water directly at the base of the plant, never over the foliage.
- Ensure good air circulation between plants; do not crowd them.
- Remove spent flowers and dead leaves immediately.
- Inspect your plants once a week, especially in cool, damp weather.
Common problems
- Gray mold (Botrytis) · Soft, gray rot covering flowers and fruit.
FAQ
Can I simply wipe off the gray mold?
No. This is a bad idea. The gray coating is the visible part that produces spores. Wiping it releases a **cloud of invisible spores** that will contaminate other parts of the plant and nearby plants. **Cut off and discard** the affected part instead.
Is Botrytis dangerous to people or animals?
_Botrytis cinerea_ is generally not considered a pathogen of people or animals. However, heavy, repeated exposure to its spores can cause **allergic reactions** or respiratory problems, such as asthma, in sensitive people.
What is the difference between Botrytis and powdery mildew?
They are easy to tell apart. **Botrytis** forms a **thick gray or brownish coating** and causes soft, wet tissue rot. **Powdery mildew** appears as a **dry white powder**, as though flour had been sprinkled on leaves, which do not immediately rot.
Why did my plant get it?
Your plant was probably exposed to a combination of three factors: **excessive ambient humidity**, **poor air circulation**, and weakened tissue, such as a spent flower or damaged leaf. This is the perfect combination for ever-present Botrytis spores to become established.
Is baking soda treatment really effective?
Yes. It is mainly effective as a preventive measure and for light infections. Baking soda changes the pH on the leaf surface, which **hinders germination of fungal spores**. In a moderate attack, it helps stop spread after the most affected parts have been removed.
Are there effective commercial fungicides?
Yes. Specific gray mold fungicides are available, often based on **copper (Bordeaux mixture)** or sulfur. For indoor use, the French guidance is to look for products bearing the wording "Emploi autorisé dans les jardins" (authorized for garden use) and follow the instructions precisely. However, better ventilation and lower humidity remain the most lasting solutions.
Can a plant with Botrytis be saved?
Absolutely, if the infection is caught early. If rot has affected only a few leaves or flowers, sanitation pruning and corrected growing conditions are generally enough. If the main stem is affected at the base, saving the plant becomes much harder.