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How to Manage Pests
UC Pest Management Guidelines
Floriculture and Ornamental Nurseries
Southern Blight
Pathogen: Sclerotium rolfsii
(Reviewed 1/02,
updated 1/02)
In this Guideline:
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SYMPTOMS
Southern blight, also called southern wilt, southern stem rot, southern root
rot and several other names, results from infection by the soilborne fungus,
Sclerotium rolfsii. The fungus survives in the soil as small (0.04-0.08
inch), tan to brown, round sclerotia. The
sclerotia resemble mustard seeds
in size and color and the fungus is sometimes referred to as the "mustard seed
fungus." Plants are attacked at the soil line or below. The fungus produces
abundant white hyphae or
mycelia around infected parts and in and on the soil. Sclerotia are formed by
the mycelia on infected plant parts and in the soil; their presence is the main
diagnostic feature of the disease. The initial symptoms are similar to other
basal stem rots (cottony rot, Rhizoctonia stem rot, etc.); discoloration of
lower leaves, wilting followed by collapse and death.
COMMENTS ON THE DISEASE
The disease is favored by warm moist soil, hence it occurs in the summer
months. The fungus has a wide host range and includes many field, vegetable and
ornamental crops.
MANAGEMENT
Soil fumigation or soil solarization (in sunny areas) are effective in killing
soilborne sclerotia. Bulbs and other planting stock may carry the fungus. The
fungus is killed by exposure to 122°F for 30 minutes and some plant
materials such as caladium tubers, iris rhizomes, and gladiolus corms can be
treated successfully with hot water.
| Common name |
| (trade name) |
Amount to Use |
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SOIL FUMIGATION |
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| A. |
METHYL BROMIDE* |
Label rates |
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COMMENTS: Methyl bromide is probably the most versatile
of the soil fumigants because of its ability to diffuse rapidly through
the soil and kill many kinds of organisms, weeds, and many seeds.
Soil generally can be planted in just a few days after removal of
plastic covers, although there are exceptions. A few plants such as
Allium spp., carnations, and snapdragons are sensitive to and
may be damaged by inorganic bromide that remains in the soil following
fumigation. Leaching the soil with water before planting is helpful
in reducing the amount of bromide in the rooting area. Apply under
plastic covers or inject by chisels if the soil is covered immediately
by plastic. |
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| B. |
METHYL BROMIDE*/CHLOROPICRIN* |
Label rates |
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COMMENTS: Inject into soil and cover immediately with
plastic tarps. See Comments above regarding the use of methyl bromide. |
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SOIL FUNGICIDE |
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| A. |
PCNB |
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(Terraclor) |
0.5-1 lb a.i./1000 sq ft |
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COMMENTS: Helpful in preventing infection when incorporated
into top 2 inches of soil. |
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Permit required from county agricultural commissioner
for purchase or use. |
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UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
R. D. Raabe (emeritus), Environmental Science, Policy, and Management (ESPM),
UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside
C. A. Wilen, UC IPM Program, UC Cooperative Extension, San Diego Co.
A. H. McCain (emeritus), Environmental Science, Policy, and Management (ESPM),
UC Berkeley
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