Cloudy weather and cool nights provide ideal conditions for Botrytis blight. When temperatures drop during the night, the colder air cannot hold as much moisture, so it condenses on the foliage and flowers, which encourages Botrytis.
Look carefully under canopies and around the crowns of for fuzzy grayish-brown spores which are easily spread on air currents and by splashing water. Sometimes, less obvious symptoms show as tan colored cankers on stems that can cause entire branches of plants to wilt, while the rest of the plant, including roots appears healthy (for a while). Botrytis blight cannot be controlled effectively with fungicides alone. An integrated approach is needed with sound cultural practices, management of environmental conditions combined with fungicide use.
- Remove old flowers to reduce sporulation.
- Space plants to allow for good air circulation and to reduce humidity within the crop canopy.
- HAF fans keep the air moving so there is less condensation.
Reduce humidity levels whenever possible, to prevent spore germination by watering early in the day, heating and venting two to three times per hour in the evening after sunset and early in the morning at sunrise. Set your program to activate the exhaust fans for a few minutes. Heat the greenhouse a few degrees and then vent the humid air. While heating and venting may sound expensive, it is worth it compared to plant losses or the cost of fungicides.
In the IR 4 Ornamental Horticulture Program, review of the literature on Botrytis Blight, they found that the following products provided excellent efficacy in numerous experiments:
- Pageant (pyraclostrobin plus boscalid)
- Daconil (chlorothalonill)
- Palladium (cyprodinil & fludioxonil)
- Decree (fenhexamid)
In addition, Heritage (azoxystrobin), Medallion (fludioxonil) and Compass (trifloxystrobin) showed good to excellent efficacy in a number of experiments. Be sure to rotate among effective products!
Leanne Pundt, UConn Extension and Tina Smith, UMass Extension
Note: There are many photos of plants with Botrytis in our photo library. Type in "Botrytis" in the key word box and check photo library under it.
