Botrytis Blight in Roses

Botrytis blight, also called gray mold, is a common disease in many ornamental plants, including roses. The University of Illinois Extension estimates that botrytis blight causes more economic losses in greenhouse-grown ornamental plants than any other infection.

Features

The Botrytis cinerea fungus causes botrytis blight in roses. The disease spends the winter in infested soil or decaying plant matter and matures during the spring, releasing infectious spores that travel through splashing water and wind to infect new plants. Botrytis blight is most active when humidity levels range between 90 and 100 percent and daytime temperatures average between 72 and 75 degrees Fahrenheit. The fungus requires water to germinate and cause infections, so the disease can be particularly devastating in outdoor plants if rain falls for several consecutive days.

Effects

Botrytis blight affects rose flowers and buds. The disease is characterized by drooping flowers or buds with blackened bases. A thick coating of gray mold later appears on the surface of the diseased tissue. Roses also develop cankers, or sunken areas of discolored and diseased plant tissue, on stems.

Prevention/Solution

Botrytis blight is controlled by removing and destroying dead plant material, which eradicates spores. Spacing plants so that they receive adequate air circulation controls the spread of botrytis blight. Keeping rose foliage dry by watering the surface of the soil rather than the leaves helps prevent botrytis blight spores from germinating. Regularly timed fungicide treatments can also prevent plants from becoming infected.

References

• University of Illinois Extension: Botrytis Blight or Gray Mold of Ornamental Plants
• Sacramento Rose Society: Botrytis Blight
• Cornell University: Botrytis Blight