See:
Greenhouse Plants, Ornamental - Gray Mold
Cause Botrytis cinerea (sexual: Botryotinia fuckeliana) and other Botrytis spp., fungi that colonize dead, dying, and wounded plant parts. From these infections they can attack healthy tissues. A moist, humid environment is ideal for pathogen sporulation and spread. Spore dispersal is stimulated by changes in relative humidity. Conidia may come from many sources. It is found everywhere plants are grown and has a wide host range wide host range including African violet, ageratum, ajuga, aphelandra, aster, begonia, caladium, calceolaria, carnation, chrysanthemum, coleus, cyclamen, fuchsia, geranium, gloxinia, hosta, Iberis, impatiens, lily, lobelia, marigold, orchid, pansy, Pericallis hybrids, petunia, poinsettia, primrose, rose, snapdragon, verbena, viburnum, zinnia, and zygopetalum. Flower petals are most susceptible at any stage of development. Blossom blight, leaf spots, and bud and stem rots are common. Leaf blights can start when infected floral tissue falls on healthy leaves. Unrooted cuttings in propagation are very sensitive since the excess water needed for rooting promotes this disease.
Symptoms Blighting of leaves and petioles is the most common symptom. Leaf lesions are brown or black in color and in most cases extended inward from the margin of the leaf, and frequently advanced until the whole leaf is involved. The invaded leaf tissue can be filled with gray mycelium and spores of this fungus.
Cultural control An integrated strategy combining environmental management, cultural practices, and fungicides will most effectively manage this disease.
- Thoroughly clean and sanitize the greenhouse before production.
- Remove all dead and dying plant parts (particularly blossoms) on and around plants in the production area. Many greenhouse growers use closed containers to minimize the amount of conidia.
- Maintain a steady, 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 (especially for zero or negative DIF) or venting around sunset may be necessary. Heating in the morning before sunup can also help prevent dew formation as air temperature increases faster than the temperature of plant parts.
- Spacing plants also allows better light penetration, reducing senescence of the lower leaves and thus helping reduce the amount of highly susceptible plant tissue.
- Eliminate weeds from the production area including inside the greenhouse and around doorways and vents outside of the greenhouse.
- Place fans in greenhouse to get better air circulation.
Chemical control Fungicides do not compensate for poor sanitation or environmental controls. Resistance to many different and multiple fungicide groups has been documented worldwide. To prevent developing resistant fungi, alternate or tank-mix materials from different groups with different modes of action. Also, limit applications from any specific group to two (2) or fewer sprays.
- Astun at 10 to 17 fl oz/100 gal water. Group 7 fungicide. 12-hr reentry.
- Broadform at 4 to 8 fl oz/100 gal water. Group 7 + 11 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. Do not apply more than twice sequentially. Group 17 fungicide. 12-hr reentry.
- Medallion WDG at 2 to 4 oz/100 gal water. Using with oils or adjuvants may damage plant. Group 12 fungicide. 12-hr reentry.
- Mural at 4 to 7 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Orkestra at 8 fl oz/100 gal. Group 7 + 11 fungicide. 12-hr reentry.
- Pageant at 12 to 18 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
- Palladium at 4 to 6 oz/100 gal water. Avoid excessive runoff to small plants, which may result in stunting and/or chlorosis. Group 9 + 12 fungicide. 12-hr reentry.
- Phyton 27 at 1.3 to 2 oz/10 gal water. Group M1 fungicide. 48-hr reentry.
- Spirato GHN at 2 to 4 fl oz/100 gal water. Use with oils or adjuvants may cause plant damage. Group 12 fungicide. 12-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 3 0.33 oz/5 gal water. Do not use with other products in the tank. 4-hr reentry. O
Reference Heald, F.D. and Dana, B.F. 1924. Notes on Plant Diseases in Washington: 1. Botrytis Diseases. Transactions of the American Microscopical Society 43:136-144.