With summer coming, so are plant diseases. One that can affect an astonishing variety of plants—from apple trees to zinnias—is Southern blight, caused by the fungus Sclerotium rolfsii.
What to watch for
Southern blight thrives in hot, humid conditions. Although the fungus can infect many plant parts—including roots and fruits—it typically shows itself as wilt resulting from rotting stems at the base of the plant. Even before the plant wilts, you’ll often see water-soaked spots on the stems.
Some plants are particularly vulnerable. Hostas may succumb in your perennial garden. Many root crops are affected, including beets, carrots, Jerusalem artichokes, parsnips, radishes, sweet potatoes, and turnips. Other victims may be cantaloupe, eggplant, peppers, snap beans, sweet corn, and tomatoes.
How it survives
One reason Southern blight can persist in soils is that it forms sclerotia: hard, rounded bodies that look like mustard or radish seeds. The disease is sometimes called Sclerotial blight for this reason. It can also remain in plant residue in the soil and spread through surface water.
What to do
As with all fungal diseases, prevention is key. Once the plants are infected, fungicides may help prevent the spread of the disease to other plants, but won’t reverse problems on plants already affected. Depending on the crop, fungicides used as soil drenches prior to planting may prevent infection. Different fungicides are recommended for different crops, however.
Immediately remove infected plants along with their roots and the surrounding soil. Do not compost! If container plants are affected, do not reuse the potting soil. If Southern blight takes hold in your garden, solarizing for several weeks using plastic during the summer may kill the fungus.
For more information about recommended fungicides:
(See page 498 for Southern stem blight, Sclerotium rolfsii)
Factsheet from the American Phytopathological Society:
Article written by Debbie Green, Extension Master GardenerSM Volunteer.