Sclerotium of Southern blight
Pathogen: Sclerotium rolfsii
Hosts Include: Ajuga, Anemone, Aquilegia, Campanula, Coreopsis, Delphinium, Dianthus, Digitalis, Helianthus, Hosta, Lathyrus, Liatris, Lilium, Limonium, Lupinus, Monarda, Penstemon, Phlox, Rudbeckia, Salvia, Scabiosa, Sedum, and Veronica.
Symptoms: Wilting, water soaked lesions on succulent stems and petioles, crown rot, plant collapse and death. Fluffy fungal mats may be present on the soil surface or on affected plant tissues. Light brown sclerotia, about the size of mustard seeds may also be present in clumps on the affected plant tissue.
Spread: This is a soil borne pathogen, movement of soil or diseased plant material spreads the disease. The pathogen can persist for extended periods of time in soil as sclerotia. During hot, humid conditions sclerotia germinate producing fungal mats that can infect susceptible hosts. Sclerotium rolfsii rarely produces spores, so dispersal by air movement is not significant.
Management: Good sanitation and pathogen exclusion are important steps in limiting disease. Carefully inspect incoming plant material for signs of disease. Remove and destroy affected plants, avoid spreading soil from infected areas. Mulch used around field grown plants or plants in the landscape may favor growth of S. rolfsii. Limit use of mulch in sites with a history of S. rolfsii problems. Fungicide applications (drenches or incorporation of granular materials) can be used preventatively to control crown rot.
Resources for additional information: Crown Rot, A Serious Disease of Hosta and Other Ornamentals, an Iowa State University Extension publication, Feb. 2000.