Plant Pathology Infobytes
October 4, 1996
Attention Home Gardeners! Stay Ahead of Southern Blight
Some vegetable diseases tend to be more pesky some years than others. This gardening season, southern stem blight, sometimes referred to as white mold, caused problems in home vegetable gardens statewide.
Gardeners who experienced crop losses as a result of southern blight in 1996 will likely suffer similar problems during the 1997 gardening season unless precautionary steps are taken starting this fall.
Southern blight is caused by a fungus. This fungus can attack and kill beans, peas, peppers, potatoes, tomatoes, and numerous other vegetable crops. Disease outbreaks are most severe during periods of wet, warm weather when temperatures range from 80 to 95 degrees.
Garden plants which have been attacked by southern blight first tend to turn yellow. This stage of the disease is quickly followed by wilting and death of the affected plant.
There are several pests which may cause plant yellowing and wilt, however it's easy to determine if southern blight is responsible. A diagnostic symptom of the disease is the presence of white fungus growth on the lower stem and nearby plant debris. This growth it most easily observed several days after a rain. Numerous smooth, round, light tan to dark brown seed-like structures called sclerotia are usually formed in the mat of fungus growth. The sclerotia generally aren't too difficult to locate and are about the same size as mustard seed.
Other than removal of diseased plants (be sure to remove the sclerotia as well), there is little that can be done to control southern blight until after the gardening season is over. Losses in future seasons can be reduced by practicing the following control recommendations:
- This fall, remove crop debris from the garden area following final crop harvest.
- This should be followed by burial of any remaining crop debris by plowing the soil to a depth of at least six inches. This practice is important since it insures that carryover sclerotia are also buried. Sclerotia serve as the source of future southern blight outbreaks, so burial means they won't be around to cause problems in the next gardening season. Crop residue burial has the additional benefit of helping to reduce the incidence of other vegetable diseases as well.
- Next spring, use corn as a rotation crop for areas of the garden where southern blight was especially severe. Corn is one of the few vegetable crops not affected by southern blight.
- Before planting, wrap lower stems of tomato and pepper transplants with aluminum foil to protect them from attack by the southern blight fungus. Check with your County Extension Office for additional details on this disease control strategy.
- Consider using a soil fungicide such as Terraclor 75 WP at planting time. This fungicide is recommended for southern blight control on vegetable crops such as tomato and pepper.
- During the season, avoid throwing soil against the lower stems of the plants when cultivating.
- Control foliar diseases since the southern blight fungus tends to first grow on fallen leaves before moving on to plant stems.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.