Southern blight (caused by Sclerotium rolfsii Sacc.) was found at two different tomato farms in Holmes County this week. Southern Blight is a serious fungal disease affecting diverse crops grown around the world, especially in tropical and subtropical regions. The disease is called “white mold” in peanuts and is a major disease across the Southeast. Since the phasing out of methyl bromide (EPA 2009) and the adoption of organic and other low-input production strategies, outbreaks of southern blight in tomatoes is becoming more common.
Early symptoms of southern blight begin with a discrete light brown, water-soaked lesion at the crown of the plant, near the soil line. As the disease progresses a wilt develops and the wilted leaves of affected plants generally remain green and hang on the plant ( photo 1). These symptoms can initially be confused with bacterial wilt caused by Ralstonia spp.
The disease is often not recognized in the field until the plant begins to wilt. Often the wilting is diurnal (during the daytime), with plants recovering at night. Under favorable weather conditions, however, the wilting can progress rapidly, become irreversible, and ultimately lead to plant death.
Unlike bacterial wilt, white mycelia can be seen near the soil line, often forming a mat around affected plant parts and serving as a clear sign of the pathogen (photo 2).
In addition, numerous tan, round, or irregular mustard-seed-sized sclerotia are produced on affected plant parts and the surrounding soil surface shortly after mycelial growth is observed (Photo 3).
At this point in the growing season control of Southern Blight is very difficult. The use of commercially available strobilurin fungicides (azoxystrobin, pyraclostrobin, and fluoxastrobin) are labeled for the control of southern blight on certain vegetables and may provide some relief, though control is difficult.
This disease requires an integrated approach for management including crop rotation, burial of crop residue and inoculum through deep plowing, use of pre-plant fungicides, and using healthy, disease free transplants.
For more information, download:
Integrated Management of Southern Blight in Vegetable Production
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