Southern Blight Information
Causal Agents
Sclerotium rolfsii
Hosts
Aster
Black-eyed Susan
Dahlia
Daylily
Gladiolus
Hosta
Impatiens
Peony
Petunia
Rose
Salvia
Viola
Symptoms & Signs
Water-soaked lesions appear on the lower portions of stems, and lower leaves may have a water-soaked appearance during early stages of disease development. As the disease progresses, plants become chlorotic and wilted. Plants infected by S. rolfsii will die if not treated.
White mycelial mats may emerge from infected tissue under warm, humid conditions. Sclerotia (survival structures) can be seen on infected tissue or the soil surface and can be tan to reddish brown, and occasionally black, in color. Under a microscope, hyphae are colorless with clamp connections and occasional septations.
When Does it Occur?
When environmental conditions are favorable, S. rolfsii frequently infects the lower stems of plants near the soil surface. The pathogen survives as sclerotia in the soil, or as mycelium on decaying organic material in the absence of hosts. Optimal temperatures for S. rolfsii growth are between 81-95° F. Saturated soil conditions are needed for sclerotia germination in the soil. The pathogen may spread to uninfected hosts throughout the season through plant debris, movement of infected plants, or soil. Mycelial mats will not survive freezing temperatures, but sclerotia can survive freezing temperatures in the soil.
Cultural Management
Use only pathogen-free plants, cuttings, or seeds. Clean all pots and planting equipment in greenhouses and use pathogen-free potting material. Avoid planting susceptible hosts in areas with a history of S. rolfsii. Thoroughly remove plant debris from greenhouses and around susceptible hosts. Improve airflow and drainage to promote drying of plant tissue and soil.
Where possible soils may be solarized to for 4-8 weeks, depending on air temperatures, to reduce viable sclerotia. Maintaining soil pH around 6.5 may slow fungal growth. Removing thatch and plant debris from the soil may also aid in suppressing S. rolfsii.
Chemical Management
Preventative fungicide applications are most effective. Rotate fungicide chemistries after each application.
| Active Ingredient(s) | Trade Name(s) | Application Timing | REI (h) | Efficacy Rating | FRAC Code(s) | Resistance Risk |
|---|---|---|---|---|---|---|
| Azoxystrobin | Heritage; Strobe; Mural | P + C | 4 | ++++ | 11 | H |
| Benzovindiflupyr | Mural | P + C | 12 | +++ ? | 7 | M |
| Cyprodinil | Palladium | P + C | 12 | +++ ? | 7 | M |
| Fludioxonil | Emblem; Medallion; Mozart TR; Spirato | P + C | 12 | ++++ | 9 | L - M |
| Fluoxastrobin | Disarm; Fame | P + C | 12 | ++ ? | 11 | H |
| Flutolanil | ProStar; SysStar | P + C | 12 | ++++ | 7 | M |
| Fluxapyroxad | Orkestra | P + C | 12 | +++ ? | 7 | M |
| PCNB | Terraclor; Turfcide | P + C | 12 | ++++ | 14 | L |
| Tebuconazole | Clearscape T&O; Tebuconazole; Torque; Enclave | P + C | 12 | +++ | 3 | M |
| Triticonazole | Trinity; Trinity TR | P + C | 12 | +++ ? | 3 | M |
1 Not all commercially available trade names are included to save space. Some products may have use restrictions. Always follow label directions for rates and use sites. Mention of specific products does not constitute endorsement.
2 P = Preventative; C = Curative
3 REI = Restricted Entry Interval
4 Relative efficacy. + = Marginally effective; ++ = Moderately effective; +++ = Effective; ++++ = Very Effective; ? = Limited information at this time.
5 Fungicide Resistance Action Committee code(s). Products sharing a code contain active ingredients with the same mode of action. Always use resistance management practices.
6 Resistance Risk: L = Low; M = Moderate; H = High, U = Unknown
