Greenhouse Plants, Ornamental - Gray Mold
Cause Botrytis cinerea, a fungus that overwinters in infected plants and debris. 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. Flower petals are most susceptible at any stage of development. Flower infections were light from 54°F to 60°F, moderate at 68°F, and heavy at 75°F. Leaf blights can start when infected floral tissue falls on healthy leaves.
Symptoms The showy membranous calyces and associated interior bracts collapse and become discolored. The disease proceeds rapidly through the compact flower clusters. As flowers dry out they drop from the inflorescence rachis. The uppermost extensions of the scape wings become infected and brown. The disease may continue down killing most of the branches of the panicle. Under moist conditions, the gray fuzzy growth of the fungus may be seen on necrotic tissues.
Large inflorescence branches may develop discrete lesions that may eventually girdle the branches. All parts of the plant distal to these lesions then die. Branch lesions are slightly depressed, tan to orange, up to 2 cm in length and show faint dark banding.
- Remove and destroy infected plant parts and debris.
- Space plants for good air circulation.
- Avoid overhead irrigation that keeps plants wet for extended periods of time.
Chemical control Tank-mix and/or alternate products with different modes of action to prevent building up resistant fungi. Limit the use of any one group during crop production.
- Astun at 10 to 17 fl oz/100 gal water. Group 7 fungicide. 12-hr reentry.
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. Group M5 fungicide. H
- 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. Group M5 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.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 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 Jackson, C.R. 1960. Crown rots and botrytis flower blight of statice. Plant Disease Reporter 44:643-645.