Botrytis Blight on Roses: How to Identify & Treatment

Are your blooms coated in gray fungus or are the flower buds drying out and browning?

Roses are ornamental plants which are grown for their scent, beauty and multiple colors. But, the roses are susceptible to Botrytis blight which can cause economic losses. This disease affects leaves, buds, bulbs and stems of the plants.

In this article, you’ll explore how to identify the rose Botrytis blight. You’ll also discover different methods to treat Botrytis blight on roses.

What is Botrytis Blight in Roses?

Botrytis blight on roses is the appearance of gray-brown mold on flowers which is caused by a fungus named “Botrytis cinerea”. These pathogens cause significant commercial loss worldwide.

This pathogen grows well at optimum temperature of 60°F. The Botrytis affect the plant at damaged or wounded parts of roses especially in a highly humid environment.

The pathogens spread usually in the form of spores which are oval and one-celled structures. These spores are formed in clusters and multiply in humid and optimal temperature conditions.

Why are Roses Highly Vulnerable?

Roses are one of the ornamental plants which are popular for their soothing natural scent and beauty. There are many reasons why roses are vulnerable to the Botrytis, some of them are:

The roses have tender, delicate and soft flower buds and petals which make them more vulnerable to different diseases.
Roses often grow in overcrowded bushy clusters which reduces the airflow between the plants.
As roses have bloomed over a long season, fresh and young flowers are always present for Botrytis growth.
Flowers are usually grown in damp and moist environment conditions.
Spores can germinate in petals even after harvesting.

Common Infection Periods

Infection Period	Plant Stage / Condition	Environmental Conditions	Susceptibility
Early Spring	New shoots, tender buds	Cool (15–20°C), high humidity	Young tissues are highly vulnerable to infection
Bud Formation & Blooming	Tight buds, partially opened flowers	Moist conditions, dew, or overhead watering	Petals trap moisture, perfect for spore growth
After Rain / Overhead Watering	All above-ground parts	Wet leaves, petals, stems	Water splash spreads spores easily
Late Fall / Autumn	Older shoots, aging blooms	Cool and damp conditions	Senescing tissues are more prone to infection
Any Time under Plant Stress	Damaged leaves, crowded plants, nutrient-stressed	Low airflow, overcrowding, wounds	Stressed plants are more susceptible regardless of season

Symptoms of Botrytis on Roses

You can observe symptoms of Botrytis blight on roses especially during cold and humid weather conditions. Here are some most common symptoms of Botrytis on roses:

Gray Mold on Petals

The Botrytis fungi attack the flower and buds which may not open yet. The fungal spores cover the whole flowers in a grayish-brown mold. You can notice the small spots on infected petals of flowers as well.

Browning Buds

New forming tender shoots and flowering buds are highly susceptible to the pathogens. The gray mold grows on buds and changes their color into brown. The pathogens block the flowers’ buds from blossoming and the petals become darker and shrink.

Stem Lesions

Stem lesion is a common sign of Botrytis blight on roses as grayish spots formed at the base of stems. These lesions weaken the stems and continue to infect the cane. You can notice the grayish mold at injured parts of plants or at sites where flowers or other parts of plants have been cut.

How to Treat Botrytis Blight on Roses

You can control the infected plants by using some simple yet straightforward and efficient solutions. Here are some of the effective ways to treat Botrytis blight on roses:

Remove Infected Buds

Cut the infected or injured portion of plants like stems, leaves or flowers once you notice the signs of illness. These damaged portions of plants act as a substrate for gray mold growth. The Botrytis reproduce a large number of spores which can infect the other parts of the rose as well.

Improve Airflow

Gardeners should maintain proper airflow inside their growth medium. The proper airflow control the gray mold even if in the humid environment.

Gardeners must introduce proper ventilation in their greenhouses. They must cut the extra branches and leaves to create a space between plants. This will also improve the air circulation as well.

Reduce Humidity

Install vents or dehumidifiers in your growth medium. These tools prevent moisture buildup. Your greenhouse must have a good drainage system to remove extra water. Don’t use overhead sprinklers as it keeps the leaves and flowers moist for several hours.

When to Use Fungicides

You can use fungicides at the injured and freshly pruned sites of plants to reduce the risk of Botrytis. Many people use fungicides at pre or post harvest stages to combat Botrytis. But, now there is emergence of fungicides resident Botrytis cinerea. It also has harmful effects on human and animal lives.

Long-Term Prevention for Rose Growers

Fungicides can give you temporary relief but after some time the Botrytis will return again. You can follow some long term habits to prevent the gray mold.

The greenhouse which has overcrowded vegetation and located at humid and cold areas are highly vulnerable to gray mold. The ideal humidity above 93% RH and the temperature about 15 to 21°C are ideal conditions for gray mold to flourish.

So, it is best to regulate the humidity between 30-60% inside your greenhouse. The lower humidity prevents any pathogens intrusion.

Correct Watering

The right watering practices can help you in the long run. Don’t use overhead sprinklers because the water stays on flowers and leaves for several hours providing a growth medium for Botrytis.

Tight buds hold water inside and increase the chances of gray mold. So, prefer drip irrigation instead of overwater sprinklers. Water your plants during day time as it helps to evaporate extra water in the presence of sunlight.

Spacing & Pruning for Airflow

Overcrowded plant areas have poor air circulation and humidity control. You can cultivate the plant bushes by following an appropriate space approach between different plants.

Always cut the dense foliage to provide more space and air to the rose bushes. Thin out your plant to reveal the centre of the plants. In this way the leaves of the plants can dry more quickly after the rainfall.

Dehumidifier Settings

Dehumidifiers maintain the humidity lower than 60% RH inside the greenhouse. The device creates a controllable environment in which you can control the environment conditions inside the growth medium.

Set your dehumidifier to regulate humidity between 30% to 60%. This prevents fungal diseases including gray mold. Make sure that humidity levels remain below 70% especially at the night time.

Fan Placement

You can place your fans slightly higher than plant bushes to improve airflow. The fans move horizontally across the plants for rose bud blight treatment.

Fan Type	Placement	Purpose
Circulation Fan	Canopy level, above plants	Gentle airflow to reduce leaf moisture
Oscillating Fan	Along aisles, alternating rows	Prevent stagnant pockets of humid air
Exhaust Fan	One end of greenhouse / high points	Remove humid air and refresh atmosphere
Intake Vent	Opposite end of exhaust fan	Ensure continuous air exchange

Greenhouse Adjustments

Botrytis multiplies in cool, humid and poorly ventilated environments. So, you should maintain the conditions inside the growth medium. Make sure the daytime environment holds 20–25°C consistently.

You must maintain the humidity below 85% RH especially during bud formation and blooming stage. You can use ventilation fans or dehumidifiers.

Conclusion

Roses are ornamental plants which are vulnerable to Botrytis because of tender flowers and stems, roses grow in bushy clusters and roses are usually grown in a humid and cold environment.

You can identify gray mold on your roses if you notice brown flowers’ buds, stem lesions and gray mold on petals.

You can use ventilation fans, Coairo dehumidifiers and greenhouse adjustments to prevent Botrytis in roses.