Greenhouse Plants, Ornamental - Gray Mold
Cause Botrytis cinerea, a fungus. The disease on Ageratum may become severe when plants are crowded and growing conditions are humid. This fungus readily colonizes senescent leaves and flower parts. There are few references about Botrytis on this plant but it does show up on host lists. An essential oil extract of A. conyzoides was active against Botrytis in vitro.
Symptoms Brown to black spots appear on leaves, stems, and flowers, which may later coalesce to involve larger areas. Under moist environmental conditions typical gray-brown spore masses of the fungus may appear.
- Avoid crowding plants and overhead watering.
- Maintain a steady, relatively dry environment by keeping greenhouse humidity below 90%. 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. If using DROP or DIP for size control, do not let humidity rise above 90%.
- Remove and destroy badly affected plants or plant parts.
Chemical control Best when used with cultural controls. Tank-mix and/or alternate products from different groups with different modes of action to prevent the build-up 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.
- Emblem at 2 to 4 fl oz/100 gal water. Use with oils or adjuvants may cause plant damage. Group 12 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 cause plant damage. Group 12 fungicide. 12-hr reentry.
- OHP 6672 4.5 F at 10 to 14.5 fl oz/100 gal water plus another fungicide. Group 1 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.
- 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.
- 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 Elad, Y., Pertot, I., Prado, A.M.C., and Stewart, A. 2016. Plant hosts of Botrytis spp. In Botrytis-the fungus, the pathogen and its management in agricultural systems (pp. 413-486). Springer, Cham.