See:
Greenhouse Plants, Ornamental - Gray Mold
Cause Botrytis cinerea, a fungus that colonizes dead, dying, and wounded plant parts. From these infections they can attack healthy tissues. A moist, humid environment is ideal for the pathogen's sporulation and spread. Conidia may come from sources in and outside the greenhouse. The fungus is found everywhere plants are grown and has a wide host range. Flower petals are most susceptible at any stage of development. Frequently colonizes flowers already compromised by other pathogens such as Sclerotinia.
Symptoms Small water-soaked lesions form on damaged petioles and spread to leaf blades. Infected flowers fade prematurely. By comparison to Sclerotinia, Botrytis lesions were not as wet and did not cause the complete collapse of flowers.
Cultural control
- Remove all dead and dying plant parts (particularly blossoms) on and around plants.
- Maintain a relatively dry environment by keeping greenhouse humidity below 90%, increasing spacing between plants for good air circulation, and taking care not to splash water on foliage during watering. Heating the greenhouse at night or venting around sunset may be necessary.
- Spacing plants also allows better light penetration, reducing senescence of the lower leaves and thus helping reduce the amount of highly susceptible plant tissue.
- Place fans in greenhouse to get better air circulation.
Chemical control Best when used with cultural controls. Tank-mix and/or alternate materials from different groups with different modes of action to prevent the buildup of resistant fungi. Limit the use of any one group during the growing season.
- Astun at 10 to 17 fl oz/100 gal water. Group 7 fungicide. 12-hr reentry.
- Chipco 26019 FLO at 1 to 2.5 quarts/100 gal water. Group 2 fungicide. 12-hr reentry.
- Decree 50 WDG at 0.75 to 1.5 lb/100 gal water. Check for phytotoxicity before using. Group 17 fungicide. 12-hr reentry.
- Phyton 27 at 1.3 to 2 fl oz/10 gal water. Group M1 fungicide. 48-hr reentry.
- Terraguard SC at 4 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Biological control
- Prestop (Gliocladium catenulatum strain J1446) at 0.33 oz/5 gal water. Do not use with other products in the tank. 4-hr reentry. O
Reference Raabe, R.D. and Hendrix, F.F. 1966. Sclerotinia blight of Gloxinia. Mycologia 58:161-166.