Disease Note.

First Report of Stem Rot of Monarda didyma Caused by Sclerotium rolfsii . G. E. Holcomb, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. Plant Dis. 78:208. Accepted for publication 29 October 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0208E.

Monarda didyma L. (bee balm, Oswego tea) is widely grown as an ornamental and medicinal plant in the United States and Europe and is available commercially as a dried tea. A severe stem rot that killed infected plants was observed on M. didyma in the demonstration herb garden at Burden Research Plantation, Baton Rouge, during July 1992. White mycelial mats and light brown sclerotia (1-1.5 mm in diameter) were seen at the base of infected stems. The fungus was isolated on 2% water agar and identified as Sclerotium rolfsii Sacc. Pathogenicity tests were performed by pouring 10 ml of blended mycelia and sclerotia on the bases of healthy plants and cuttings (one 10-day-old fungal culture, grown on potato-dextrose agar, blended in 100 ml of distilled water). Inoculated plants and uninoculated controls were held in a dew chamber at 28-30 C for 3 days, at which time stem rot had developed. The pathogen was reisolated from inoculated plants. S. rolfsii has been reported on several other species of Monarda (1), but this local disease outbreak is its first recognized occurrence on M. didyma