Fwd: P&PDL reply to log #98-1054 (Stegeman)
I apologize for the length of this file-but I thought it might interest many
of you. I submitted a large 'Sum and Substance' that I thought had Southern
Blight or Crown Rot to Purdue University today for diagnosis and suggestions
on control. I am attaching their reply.
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PLANT & PEST DIAGNOSTIC LABORATORY
765-494-7071 FAX: 765-494-3958
World Wide Web (http://www.btny.purdue.edu/ppdl/)
This message contains information on a sample submitted to the P&PDL.
Diagnosis and Control Recommendations
1202 LAKE DR
CHESTERTON IN 46304
1202 LAKE DR
CHESTERTON IN 46304
SAMPLE NUMBER: 98-1054
Date completed: 7/22/98
Date reply printed: 7/22/98
CULTIVAR: sum and substance
SAMPLE CONDITION: Good
INFO DESIRED: Problem ID; Control measures
Sclerotium rolfsii was confirmed on your Hosta sample. I have enclosed a
photocopy from one of my ornamentals references for your information .
The following article which appeared in a 1994 newsletter is one of the most
thorough I have seen on this disease problem:
Southern Blight: a Destructive Summer Disease in the Vegetable Garden and
Mary Ann Hansen
Instructor and Plant Clinic Manager
Department of Plant Pathology, Physiology, and Weed Science and the Department
Virginia Polytechnic Institute and State University, Blacksburg Virginia
Most plant pathogens attack only one or a few closely related plant species,
but this is not the case with Sclerotium rolfsii, the fungus that causes a
disease called "southern blight". This fungus is an aggressive stem rotter of
a wide range of species, including not only vegetables and flowers, but also
some field crops and fruit trees. It is favored by high temperatures and high
humidity, hence its prevalence in the southern United States. Now is the time
to be looking for symptoms of this destructive disease in your vegetable
garden, field, or landscape.
Sclerotium rolfsii is a soil-borne pathogen that infects stems of susceptible
plants at the soil line. The fungus quickly girdles the stem, causing a dark
brown basal stem rot and an overall wilt from which the plant does not
recover. Although other pathogens can cause a basal stem rot, Sclerotium
rolfsii is easily recognized by the ropy or fan-shaped white mycelium and the
mustard-seed-like "sclerotia" it produces on the surface of the rotted tissue
or on surrounding soil. The sclerotia are resting structures of the fungus
that allow it to survive the winter in the soil. The tough, exterior "rind"
of the sclerotia is initially white, but gradually turns a golden color, and
later brown; the interior of the sclerotia is white. Sclerotia can withstand
cold temperatures down to 14#251#F. They germinate in summer, producing
mycelium that grows on the surface of stems of susceptible species until it
eventually penetrates the stems and causes rot. Sclerotia can survive for !
several years in soil until a suit
able host plant is present.
Controlling southern blight is difficult because the pathogen has a wide host
range and because the sclerotia persist in the soil. Many vegetable crops are
susceptible to this disease, but the species we most frequently diagnose with
southern blight are tomatoes and peppers. We also occasionally see the
disease in beans and carrots. Other vegetable crops reported to be
susceptible include artichoke, beet, Brussels sprout, cabbage, cauliflower,
sweet corn, cucumber, eggplant, endive, garlic, gourd, lettuce, cantaloupe,
parsley, pea, okra, onion, potato, pumpkin, radish, squash, sweet potato,
turnip, and watermelon. Because the pathogen has such a wide host range,
rotation is not a feasible method of disease control in the vegetable garden.
It is important to recognize the symptoms of this disease early to implement
other cultural controls. If affected plants are removed before sclerotia
form, the amount of overwintering inoculum can be reduced. Remove plants and
soil to a depth of about 6 inches and a radius extending 6 inches beyond the
edge of the affected area. If the disease is not diagnosed until the
sclerotia have already formed, it would still be worthwhile to remove affected
plants and surrounding soil to try to remove the sclerotia. It is also
important to avoid moving soil from a southern blight-infested area to other
areas of the garden or field since sclerotia can be moved with the soil. Be
aware of this when roto-tilling. If you have had serious problems with
southern blight in the past, you may consider planting the vegetable garden to
a small grain for two years to reduce fungal inoculum before replanting
vegetables. Increasing the organic content of the soil is also reported to
cidence of the disease, as is addi
tion of nitrogenous fertilizer, such as ammonium nitrate.
Many floral crops are also susceptible to the disease, but it is possible to
plant flower species that are immune to the disease. In the Clinic we have
diagnosed southern blight in the following ornamental plants: Ajuga, anemone,
aster, chrysanthemum, coneflower, tickseed, dahlia, Dichondra, Eupatorium,
Hosta, Impatiens, iris, Jacob's ladder, periwinkle, Madagascar periwinkle,
phlox, Physostegia, Rudbeckia, Salvia, and snapdragon. Many other flowers are
susceptible as well, If you have had southern blight in your flower garden in
the past, you would be well advised to plant species not reported to be
susceptible to the disease. Some plants from which you can choose include
Abutilon, hyacinth, Alyssum, bells of Ireland, lavender, Cleome, Mertensia,
cockscomb, Portulaca, four o'clock, primrose, English daisy, statice,
Fritillaria, tansy, globe amaranth, Freesia, Gypsophila, and Geranium (wild
The fungicide, Terraclor, is registered for control of southern blight in some
vegetable and ornamental corps, but it is mainly for commercial use.
Terraclor is not packaged in a size container affordable to homeowners, It
is used preventatively as a soil drench at transplanting or seeding and is not
for use after the crop is in the ground. The cultural controls discussed
above are the best means of controlling southern blight in the home landscape.
One additional note:
Although Terraclor is the best fungicide for protecting healthy plants from
infection by Sclerotium rolfsii, Daconill 2787 and Clearys are also labeled.
However, if you cannot get ahold of Terraclor or do not wish to use a
fungicide, there is a biocontrol alternative that has been successful for
controlling this disease on peanuts in Texas. Corn meal is top dressed or
lightly disced into the soil for control of Southern Blight on peanuts. A
naturally occurring soil-borne fungus called Trichoderma grows on the corn
meal and helps to control the Sclerotium rolfsii.
There is now a commercially produced biolcontrol product called 'Root Shield'
which is used in greenhouses to help protect roots of container grown plants
from root rot pathogens. The biocontrol agent in the 'Root Shield' product is
a Trichoderma sp.. I do not know if the 'Root Shield' would be available to
you as a homeowner or whether it is labeled for use on Hosta.
I hope this information will be of some help as you consider your control
options. If you wish to discuss this further, you may contact me at
Gail Ruhl/Plant Disease Diagnostician
Most Purdue publications are available electronically at the following
A hard copy of your response and any enclosures are being sent to you
via campus mail or US mail.
Identification No. 1
COMMON NAME: Southern blight
AGENT/SPECIES: Sclerotium rolfsii
CERTAINTY OF ID: Confirmed
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- From: "Michael D. Cook" <email@example.com>