Group Title: ARC-A research report - Agricultral Research Center-Apopka ; RH-78-4
Title: Facts and suggestions for producing and maintaining pathogen and pest-free soil media
Full Citation
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 Material Information
Title: Facts and suggestions for producing and maintaining pathogen and pest-free soil media
Series Title: ARC-Apopka research report
Physical Description: 4 p. : ; 28 cm.
Language: English
Creator: Knauss, J. F ( James Frederick ), 1938-
Agricultural Research Center (Apopka, Fla.)
Publisher: University of Florida, IFAS, Agricultural Research Center
Place of Publication: Apopka FL
Publication Date: 1978
Subject: Soils -- Composition -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: J.F. Knauss.
General Note: Caption title.
 Record Information
Bibliographic ID: UF00065899
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 70636084

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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
of Florida



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

many ways.

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,

benches, etc.

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.

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