Heat Treatments to Control Soil-Borne Pests

This promotes plant vigor, increases yield and quality, and decreases 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.

Timing

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.

Recontamination

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.