Soil Fumigation

 In fields that are infested with soilborne plant pathogens and/or plant parasitic nematodes, soil fumigation is one method of reducing pest populations sufficiently to produce high quality and high yielding vegetable crops. Soil fumigants must be applied properly, and an aeration period is necessary between soil fumigant application and planting of the crop; otherwise, plant injury will occur.
 Fields to be treated with soil fumigation must be prepared sufficiently to seed a vegetable crop. The soil should contain little or no crop debris, be free of clods, and soil moisture must be adequate to support seed germination. If soil moisture levels are low, fields should be irrigated to bring the moisture to a satisfactory level. If fields are not properly prepared, soil fumigation will not be effective due to lack of penetration of all soil particles by the gaseous fumigant
 Soil temperature at the 6-inch debth should be in the range of 50 to 80¡F (10-26.7¡C). Fall months are ideal for fumigation. Fumigation in the spring is less desirable because some fumigants may linger in cool, wet soil and increase the likelihood of reduced seed germination or injuring young plants.
 The following multipurpose soil fumigants should be used to provide disease and nematode control:

chloropicrin--50 gal/A, or dichloropropene (Telone II)9-12 gal/A, or dichloropropene + chloropicrin (Telone C-17)--30 gal/A, or dichloropropene + chloropicrin (Telone C-35)--13-20.5 gal/A
metam-sodium (Vapam HL)--37.5-75 gal/A, or
metam-potassium(K-PAM HL)--30-60 gal/A, or
methyl bromide (Terr-O-Gas 67, MC-33)--225-350 lb/A

 A plastic film seal is needed when methyl bromide is used, and when it will increase the efficacy of all the above treatments. Other soil fumigants are injected to a depth of 6 to 8 inches. Immediately after application, soil should be dragged. rolled, or cultipacked to delay loss of fumigant. Metam-sodium is water soluble and can be injected and applied via irrigation systems (solid set sprinkler or drip/trickle). Metam-sodium must be injected for the entire time that the field is irrigated (apply an acre inch of water). Rinse the irrigation system with clean water only long enough to clear the system. Too much rinsing or a heavy rainfall within 24 hours of application will reduce the efficacy of the treatment.
 At least 2 to 3 weeks should intervene between the application of most soil fumigants and the time a crop is planted. See manufacturer°s label recommendations for specific crops and fumigants. Methyl bromide requires only 2 to 7 days of waiting after removal of the tarp.
 One week after application, work soil to a debth of several inches so that gases may escape. Severe injury or killing of sensitive plants may occur if the fumigant has not sufficiently dissipated. To determine if it is safe to plant into fumigated soil, collect a soil sample from the treated field (do not go below the treated depth). Place the sample in a glass jar with a screw top lid. Firmly press numerous seeds of a small seeded vegetable crop (lettuce, radish, etc.) on top of the soil and tighten the lid securely. Repeat the process in another jar with nonfumigated soil to serve as a check. Observe the jars within 1 to 2 days. If seeds have germinated, it is safe to plant in the field. If seeds have not germinated in the fumigated sample and have germinated in the nontreated sample, then the field is not safe to plant. Rework the field and repeat the process in a few days. Since nitrifying bacteria are reduced by the fumigants, at least 50 percent of the nitrogen in the initial fertilizer application should be in the nitrate form.

Information provided is intended for consideration by the user, but is not intended to be a recommendation. Production decisions should be based on consideration of many types of information (scientific, experiential, economic, legal, etc.) available to the user.

Where trade names are used no discrimination is intended, and no endorsement by the Cooperative Extension Service is implied.

 Dr. Alan A. MacNab, Professor, Plant Pathology
Penn State College of Agricultural Sciences
211 Buckhout Lab, University Park, PA 16802

Updated: March, 2003; EMH
Loaded: June, 2003; AAM

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