See:
Greenhouse Plants, Ornamental - Gray Mold
Cause Botrytis cinerea, a fungus that survives as mycelium, conidia or sclerotia and colonizes dead, dying, and wounded plant parts. From these infections fungi can attack healthy tissues. A moist, humid environment is ideal for the pathogen's sporulation and spread. Conidia are transported by air currents, insects, or water splash to plant surfaces. Conidia may come from sources inside and outside the greenhouse. After germination, spores enter the host through wounds or natural openings. It is found everywhere plants are grown and has a wide host range. Flower petals are most susceptible at any stage of development. Latent infections can result in losses after cutting and during shipping. Infection of tissues produces ethylene which in turn induces susceptibility and enhances senescence of flowers.
Symptoms Brown water-soaked spots on leaves or petals, which later produce a gray-brown mass of spores. Petals may turn brown and also can be covered with the gray fungal growth. Infected buds may fail to open and sometimes abort.
Cultural control
- Remove old flowers and wounded plants from growing area. Place into closed containers if not removed from the greenhouse immediately.
- Lower greenhouse humidity below 85%. Heat and vent to expel moist air to reduce humidity especially when flowers begin to show color.
- Maintain good air circulation.
- Space plants to allow good air circulation and get light to lower leaves.
- Water such that plants are not wet for extended periods of time.
- Store flowers for shipping in conditions close to freezing.
- The use of ethylene blockers (such as EthylBloc) before shipping may be helpful.
Chemical control Use foliar sprays along with cultural controls. Do not use one chemical exclusively. Tank-mix and/or alternate products from different groups with different modes of action to prevent the buildup of resistant fungi.
- 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.
- Daconil Weather Stik at 1.38 pints/100 gal water. Avoid blooms. Group M5 fungicide. 12-hr reentry.
- Mancozeb-based products can be used as mixing partners and provide some protection. Group M3 fungicides. 24-hr reentry.
- Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
- Medallion WDG at 2 to 4 oz/100 gal water. Use with oils or adjuvants may damage plant. Group 12 fungicide. 12-hr reentry.
- Nu-Cop 50 DF at 1 lb/100 gal water. Discolored foliage or blooms have been noted. Group M1 fungicide. 48-hr reentry.
- Orkestra at 8 fl oz/100 gal water. 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.
- Phyton 27 at 1.3 to 2 oz/10 gal water. Group M1 fungicide. 48-hr reentry.
- Sil-Matrix at 1 to 4 quarts/100 gal water plus a nonionic surfactant. 4-hr reentry. O
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-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 0.33 oz/5 gal water. Do not use with other products in the tank. 4-hr reentry. O
References Edney, K.L. 1967. The development of Botrytis cinerea on cut flowers of carnation. Annals of Applied Biology, 60:367-374.
Seglie, L., Spadaro, D., Trotta, F., Devecchi, M., Gullino, M.L., and Scariot, V. 2012. Use of 1-methylcylopropene in cyclodextrin-based nanosponges to control grey mould caused by Botrytis cinerea on Dianthus caryophyllus cut flowers. Postharvest Biology and Technology 64:55-57.