Cloudy, cool and rainy weather conditions that result in low light and humidity, combined with many of our greenhouse crops being in full flower can lead to Botrytis blight outbreaks.
Crops like geraniums, gerbera daisy, petunias, fuschia and calibrachoa, to name just a few, can be especially vulnerable to this disease because they have a full flower canopy at this time and most greenhouses are filled to the maximum allowable space.
Remember that Botrytis is a fungal disease that can cause leaf spots, petiole blighting and stem cankers on many different annuals and perennials. It will produce large masses of fuzzy-looking spores that are most often called gray mold. These spores or conidia will be spread on wind currents and can readily travel from infected to uninfected plants in that manner. The spores can survive for upwards of 21 to 24 days before they germinate on a plant.
Michigan State University Extension suggests these cultural control practices that will reduce the conditions that favor Botrytis infections:
- Reducing the relative humidity in the greenhouse below 85 percent
- Making sure plants do not remain wet for six or more hours in a 24-hour period
- If possible, heat and vent on mornings and evenings for at least a half-hour or more to reduce humidity, thus removing the humid, warm air and allowing for plant surfaces to dry.
Click here to read the full MSU article on botrytis blight conditions expected in greenhouses.
Source: Michigan State Extension