Heat Treatments to Control Soil-Borne Pests
Gary W. Moorman, Professor of Plant Pathology
The objective of heat treatment of soil is to reduce the numbers of weeds, insects, and disease-causing organisms in the soil and thereby promote plant vigor, increase yield and quality and decrease the need to use pesticides later in the production cycle. Soil treatments complement good disease control but do not replace the use of disease-free seed, cuttings, and transplants nor lessen the need for proper sanitation practices. Equipment is available to generate steam or aerated steam in the field or steam generating facilities used to heat greenhouses or other structures can be modified to treat soil brought near the facility.
The best time to treat is in the fall while soil temperatures are above 55F (13C) at a 6 inch (15.2 cm) depth and soil moisture is 50-85% of field capacity. Wet soil reduces the effectiveness of treatment because heat does not penetrate well. On the other hand, pests in dry, cold soil are usually in a resting state very resistance to treatment.
General Procedure In Plant Beds
In the fall, disk or rototill the soil and allow some time for the organic debris to rot, usually at least 7-10 days. Soil moisture should be 50-85% of field capacity and soil temperature above 55°F (13°C) at a 6 inch depth (15.2 cm). Either inject the steam directly into the soil or cover the area with a canvas tarp and pipe the steam under the tarp.
General Procedures For Potting Soil
Soil should be on a surface that will allow the soil to be moved without recontaminating it with untreated soil (on a wooden, metal, asphalt or concrete surface or plastic tarp). The layer of soil must be no deeper than 6 inches (15.2 cm) at any point. Cover the pile with a canvas tarp and pipe the steam under the tarp.
Monitoring The Temperature
Place a thermometer near the edge of the area or pile to be treated and another in an area away from the edge but close enough to be able to be read as the heating continues. Once the desired temperature is reached on the edge (where heat will be lost quickest) and within the area treated, THEN begin timing the treatment .
Pests inadvertently added to treated soil have no competition and may cause more damage than they normally could in untreated soil. Disinfest all tools, flats, and equipment that will be used to handle the treated soil. Do not walk or drive on treated soil.
|Steam||Heat to 180-200°F for 30 min.|
|Aerated steam||Heat all soil to 165°F for 30 min.|
|Dry heat||Heat all soil to 180-200°F for 30 min.|
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
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