Landscape - Southern Blight

Southern blight is a devastating disease that can quickly kill herbaceous plants in the landscape. The following is information on this disease from the University of Maryland.

With the high temperatures (90 +ºF) that showed up on June 7, 8 and 9th and high humidity, we may start to see plants collapsing with Southern blight.

This fungal blight is caused by Scerotium rolfsii. The fungus can attack most herbaceous perennials. It is active only during hot weather, so plants can grow well in infested soil during most of the growing season, and only become damaged during the hottest part of the summer.

The first symptoms seen are wilting and collapse of individual stems or entire plants. Close inspection of the stem at the soil line reveals white mycelium (strands of fungus growing on the stem and mulch or soil surface), and small (1/8 to 1/6 inch), tan spherical sclerotia that resemble mustard seeds. The sclerotia are white when first formed and gradually, over several days, turn brown. Roots of infected plants are typically unaffected and survive helping plants recover the next season. Cortical decay of the stem at the soil line is common during hot, humid weather. Southernblight is commonly found on many ground covers; including Lysimachia, Ajuga, and Plumbago. It is capable of blighting most herbaceous perennials, vegetables, annuals, herbs and even turf and woody plants.

Management Strategies: The basis for control of Southern blight is to reduce the number of sclerotia surviving in the upper few inches of the soil. During the growing season, remove blighted plants and the mycelium clinging to stems and mulch. Deep cultivation can provide good control by burying the sclerotia. The cornerstone for control of all blight diseases is sanitation both during the growing season and in the fall. Wilted and blighted plants and plant parts should be promptly removed from the garden. Do no compost material killed by southern blight (Sclerotium rolfsii) or white mold (Sclerotinia) because the sclerotia of these fungi may survive composting.

Information from the June 13, 2008 edition of the TPM/IPM Weekly Report for Arborists,
Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension.