Cause and symptoms

Title: Stem rot of agronomic crops and vegetables (southern blight, white mold)
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066856/00001
 Material Information
Title: Stem rot of agronomic crops and vegetables (southern blight, white mold)
Series Title: Plant Pathology Fact Sheet PP-4
Physical Description: Book
Language: English
Creator: Kucharek, Tom
Affiliation: University of Florida -- Florida Cooperative Extension Service -- Department of Plant Pathology -- Institute of Food and Agricultural Sciences
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1979
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00066856
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 51334498

Table of Contents
    Cause and symptoms
        Page 1
        Page 2
Full Text

Plant Pathology Fact Sheet

Stem Rot of Agronomic Crops and

Vegetables (Southern Blight, White Mold)
Tom Kucharek, Professor and Extension plant Pathologist, 1979, Revised
Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean

Cause and Symptoms


Stem rot caused by the fungus Sclerotium
rolfsii (Athelia rolfsii) occurs primarily in broad-
leaf (non grass) crops. In Florida, peanuts com-
monly are infected by this fungus causing se-
vere crop damage, other crops that incur this
disease either sporadically or fairly commonly
include tomato, pepper, tobacco, watermelon,
potato, eggplant, beans, okra and soybean. In
addition, seedling fruit crop trees such as
apples and citrus are infected occasionally.

This disease becomes severe when con-
ditions are wet and warm (80 95 F.). Peanuts
and soybeans usually show symptoms after the
crop canopy covers the soil and after periods
of frequent rains or irrigation. Early symptoms
often include an obvious discoloration of leaves
on a few branches (Figures 1 and 2). During wet
periods, a white fungus growth can be seen on
the lower stem near the soil surface and on or-
ganic debris on the soil. (Figure 3). Later mus-
tard seed-sized sclerotia are associated with the
fungus growth (Figure 4). At first, the sclerotia
are white; later, they turn orange, reddish or
brown. If dry conditions occur, the white fun-
gus growth will not be seen but the sclerotia
may be present if they have had time to form.
As the disease progresses, entire plants are
killed often in spots within the field or in a lin-
ear fashion following the row.

Crop rotation with grass crops, including pas-
tures where possible, is a highly effective con-
trol measure if the susceptible crop is not
planted in the same field more than once every
four years. Limited land availability often de-
ters effective control for this disease. Use a bot-
tom plow to bury organic debris and the scle-
rotia mentioned above. Sclerotia are the sur-
vival structures for this fungus but they do not
survive as well when buried at least 6 inches
deep. Also, organic debris remaining on the soil
surface offers a food base for this fungus.

Other control measures that should be
considered are wider spacing between plants
and roguing infected plants. When roguing
plants, place them immediately in a wagon or
sack and include the surrounding organic de-
bris. Then burn this diseased material. An al-
ternative to roguing would be the use of a pro-
pane torch or similar device in the field. Aim
the flame at the soil surface and lower 10 inches
of stem. The use of roguing or torching may be
more suitable for small plantings or when first
signs of the disease appear.

Chemical control is used in certain situ-
ations. Substantial control can be achieved for
peanuts with several mid-season fungicide
spray programs. On vegetable crops, the use
of multipurpose soil fumigants such as Vapam
or methyl bromide/chloropicrin will control


the stem rot fungus as well as other disease
causing fungi when these chemicals are used
prior to planting. Solarization of soil suppresses
S. rolfsii.

Figure 1. Wilting of leaves and branches in

Figure 2. Wilting of leaves in soybeans


Figure 3. White mycelial growth at base of
soybean stems.


Figure 4. Mycelial growth and sclerotia on
base of stem of okra plant.

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