| Material Information
||Facts and suggestions for producing and maintaining pathogen and pest-free soil media
||ARC-Apopka research report
||4 p. : ; 28 cm.
||Knauss, J. F ( James Frederick ), 1938-
Agricultural Research Center (Apopka, Fla.)
||University of Florida, IFAS, Agricultural Research Center
||Place of Publication:
||Soils -- Composition -- Florida ( lcsh )
||government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )
||Statement of Responsibility:
| Record Information
||University of Florida
||All rights reserved by the source institution and holding location.
||oclc - 70636084
The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
FACTS AND SUGGESTIONS FOR PRODUCING AND MAINTAINING
PATHOGEN AND PEST-FREE SOIL MEDIA
J. F. Knauss
University of Florida, IFAS
ARC-Apopka Research Report RH-78-4
The nature and condition of soil media can often be the determining
factor in the production of quality foliage plants. It is fact that the
soil medium may be the source of devastating plant pathogens and pests.
Growers who knowingly employ media components that are infested with
pathogens or pests will most assuredly be faced with production problems
later. Chemicals applied to control these problems will usually only
reduce the pathogen or pest population and will at best be mainly suppressive.
This all adds up to repeated applications and increased costs throughout the
production of the crop. The most intelligent approach is to eliminate the
pathogens and pests from the soil medium before planting and to prevent any
subsequent reintroduction into the clean soil medium.
It is essential then to start with a pathogen and pest-free soil medium.
Assurance of this may be achieved in the following ways:
1. Prepare your soil mixes employing only pathogen and pest-free
components. Prevent recontamination.
2. Buy and employ "clean", commercially-prepared mixes.
3. Treat your own prepared soil mixes by chemical fumigation.
4. Treat your own prepared soil mixes by heat sterilization.
The components you employ in your soil mix might have been pathogen and
pest-free when produced or dug, but what precautions have been taken against
recontamination during transport or storage? Recontamination can occur in
If you buy a commercially-prepared soil mix, the supplier and producer
of the prepared soil mix also had to face and guard against the possibility
of recontamination. It is especially important that if you contemplate
obtaining soil media advertised as pathogen and pest-free, that you find out
just how freedom from pathogens and pests was either produced or determined.
One can only be assured that a soil medium is free of pathogens and pests
when it has been properly fumigated or treated by heat. The details of both
methods are thoroughly discussed in Manual 23 of The University of California -
Berkeley, entitled, "The U.C. System for Producing Healthy Container-Grown
Plants". This publication should be consulted for further details.
The most effective method for cleaning up a soil medium of pathogens
and pests is by steaming. This is possible because pathogens and pests are
heat sensitive. The standard recommendation where free-flowing steam is
employed is to treat at 1800F for 30 minutes. The temperature should be
checked at the coolest part of the medium, or put more simply, at that area
of the soil mass that heats up last. In reality, when soil media are treated
with free-flowing steam they are usually treated at 2120F for a good portion
of the heating period. Soil media should never be allowed to "Over-Steam",
that is, to be treated at or above 1800F for extended periods of time. This
is disadvantageous and may cause toxicity problems later.
Where steam treatment of soil media is employed utilize the following
1. Prior to steaming, maintain all media components in a moist
condition. This activates the pathogens and pests and makes
them susceptible to heat. It also allows the steam to move
more uniformly throughout the soil mass.
2. With an accurate thermometer, test and record the temperature
several times during treatment.
3. Store and handle steam-treated soil media in a manner that
will prevent recontamination.
4. Place the steamed soil media only in new or disinfested pots,
5. Whenever possible, plant only pathogen-free plant material.
6. Utilize pathogen and pest-free tools and equipment.
7. Promote and practice effective sanitation.
Treatment of soils with free-flowing steam is not without some problems.
Paramount among these is the fact that treatment at 180-2120F is non-selective
and eliminates natural soil competitors in addition to pathogens and pests.
This creates what has been called a "Biological Vacuum", a condition that
allows pathogens, if reintroduced, to grow rapidly in the treated soil medium.
In recent years, a method of lowering the treatment temperature by injecting
air into the steam has proven to be effective in elimination of pathogens and
pests from soil medium without killing all the soil competitors. In a sense
the method, called "Aerated Steam", kills the bad guys while leaving some of
the beneficial, competitive types.
Aerated steam sterilization probably provides the best all around method
for soil medium treatment. The fact that the temperature can be maintained
anywhere within the required levels of 145-1650F for the 30 minute treatment
period cuts down on fuel costs. The process in comparison to free-flowing
steam is less dangerous to workers and has a much quicker cool-down time,
especially if the air is allowed to continue to run after the steam is turned
off. Aerated steam also reduces the chances of toxic elements accumulating
after treatment. Lastly, soil competitors saved from destruction by the
lower treatment temperatures serve to reduce the recontamination problem.
Growers seeking additional information on aerated steam should write
the following researchers and request their assistance. Both gentlemen
are experts in this area of soil treatment.
Dr. K. F. Baker Dr. R. A. Aldrich
USDA Dept. Agric. Engineering
3420 S.W. Orchard St. .249 Agric. Engineering Building
Corvallis, OR 97330 The Penna. State University
University Park, PA 16802
This public document was promulgated at an annual cost of $14.84 or
3.0 cents per copy to inform county and state extension personnel,
foliage growers, marketers and allied trades of research results
and improved practices in ornamental horticulture.