Symptoms of Disease Infection

Botrytis Blight, or gray mold, is a common and prevalent disease on a wide variety of ornamental and cut flowers, both in outdoor or greenhouse environments. This disease is caused by the fungal pathogen, Botrytis cinerea, which has a wide variety of hosts and is spread by wind.

Botrytis can infect flowers, or leaves at any stage, but older, aging plant tissues, or new tender growth tissues are more susceptible. Early signs of infection on flower petals or leaves are soft, tan, water-soaked lesions. Infected areas then develop fuzzy gray spores indicative of Botrytis gray mold. The fungus, once inside blossoms and buds, can then spread into leaves and stems, causing die-back.

Conditions for Infection

The optimum conditions for Botrytis cinerea to grow and reproduce are cool temperatures and prolonged leaf wetness periods. Botrytis most often occurs in spring and fall, where warm days and cool nights can produce condensation on leaves and flowers. Rainy periods, high humidity or overhead irrigation can result in botrytis infection at any time though. The Pest Prophet app can help track weather conditions (temperature and leaf wetness) for a given micro-climate , and help determine risk of botrytis infection.

Management Strategies

There are several cultural practices that can be used to reduce risk of botrytis infection on flowers. Increasing plant spacing can help improve air flow, which can reduce duration of leaf wetness periods and improve spray coverage if fungicides are needed. Dead, and older plant material should be removed from the field or greenhouse, along with other culls and plant debris. Infected flowers, leaves or stems should be removed from the field or greenhouse, in order to reduce sources of inoculum.

Fungicides can be used to prevent infection as well. There are variety of different modes of action which can be effective in preventing Botrytis infection and slowing its spread after infection has occurred. Rotations are recommended to avoid resistance. Some classes of fungicides can also be applied post-harvest on cut flowers. During periods of optimal conditions for botrytis growth, preventative fungicides might be needed.

Greenhouse Management

Botrytis blight or gray mold can also affect flowers grown in greenhouses. Management steps should be taken to reduce humidity and avoid leaf wetness, especially during cooler times of the year. A combination of heating and ventilation should be used to ensure optimum growth of plants while avoiding botrytis infection. Sanitation techniques to avoid sources of botrytis inoculation are especially important in greenhouses.

Read more about Botrytis related disease: Complete Guide to Botrytis (Gray Mold)