Clean, weed-free field production. |
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Soil fumigants are used to kill weed seeds and underground plant parts as well as nematodes and disease organisms before planting in areas where high-value crops are to be planted. Fumigation is most commonly used for preparation of seedbeds but is sometimes used to treat potting soil or certain high-value areas in a landscape. Especially careful attention must be given to label directions concerning soil temperatures and preparation, time between treatment and planting, and safety instructions.
Soil fumigation will be most effective if done in late summer or early fall because the soil temperature is relatively high at this time. All fumigants are most effective if the soil temperature is above 55 degrees F at the time of application. Areas that must be fumigated in the spring can be covered with plastic for several days prior to treatment to raise the soil temperature. If needed, the same plastic can then be used to cover the treated area after application of the fumigant.
Proper soil preparation is essential for effective soil fumigation. The soil should be plowed and cultivated to a uniform loose texture to a depth of 6 to 12 inches. At the time of application, the soil should be free of clods and fresh organic debris, moist enough for seed germination, and at a temperature suitable for the product being used.
After fumigation, the grower must wait the length of time specified on the product label before planting. Planting too soon can result in the injury or death of the crop.
Some fumigants kill beneficial soil fungi that form mycorrhizae, a root-fungus association that is needed for normal growth by most plants. The fungi that form the association with most conifers and a few deciduous trees, such as birch and oak, are spread by airborne spores. They reinfest fumigated beds quickly. However, the fungi associated with most deciduous plants produce their spores in the soil. It takes much more time for them to reinfest fumigated soil. Methyl bromide is the fumigant that causes the most damage to populations of mycorrhizae.
Soil fumigants that are commonly used in nurseries include dazomet (Basamid), methyl bromide / chloropicrin (Brom-O-Gas, Dowfume, Terr-O-Gas), and sodium methyl dithiocarbamate (Vapam, VPM).
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Clean, weed-free field production. |
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| Basamid Granular (dazomet) Producer: BASF | ||
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| Application rate: | 347 lb ai/A. | |
| Formulation | per acre | per 1000 sq ft |
| 99G | 350 lb | 8 lb |
| Solubility: 2000 ppm (high).
Stability: Easily lost through volatilization. Mode of action: Degrades to methylisothiocyanate, formaldehyde, hydrogen sulfide, and monomethylamine, which interact in the presence of moisture and disrupt biological functions of soil organisms. Crop uses: Site preparation for high-value crops, primarily seed or liner beds. Kills weeds, their seeds, and some disease-causing organisms. Weed control strengths: Soil fumigant for preplant control of most weeds. Weed control weaknesses: Provides poor control of legumes, sedges from seed, and morningglories. Use recommendations: Soil temperature must be above 45 degrees F and should be between 55 and 65 degrees F. The seedbed should be prepared prior to application, with adequate moisture for good plant growth for 7 to 14 days before treatment. Germinating weed seeds are more easily controlled than dormant seeds. Seal the surface as soon after application as possible by compacting the surface, irrigating, or covering with plastic. All gaseous residues must be removed prior to planting. Soil moisture, temperature, and structure determine the time required between treatment and planting (normally from 10 to 30 days). Notes: Do not apply to growing crops. Conduct a germination test of treated soil before planting. Vapors from treated soils may injure plants growing in enclosed structures. Do not apply within 4 feet of growing plants or closer than the drip line of trees and large shrubs. Basamid also has nematicidal, fungicidal, insecticidal, and slimicidal activity. | ||
| Brom-O-Gas, Terr-O-Gas (methyl bromide, chloropicrin) Producer: Great Lakes Chemical Corp. | ||
| Application rate: | 240-450 lb ai/A. | |
| Formulation | per acre | per 1000 sq ft |
| 98% L | 240-450 lb | 5.5-10.3 lb |
Stability: Highly volatile. Mode of action: Highly reactive fumes inhibit respiration, resulting in disruption of biochemical processes. Crop uses: Site preparation for high-value crops, primarily seed or liner beds. Kills weeds, their seeds, and some disease-causing organisms. Weed control strengths: Controls most broadleaved weeds and grasses. Weed control weaknesses: Provides poor control of legumes, Carolina geranium, morningglories, bindweed, and sedges. Use recommendations: Soil preparation is critical for obtaining good results. The seedbed should be prepared prior to application, free of clods and undecomposed organic matter, and with adequate moisture for good plant growth. The chemical must be injected into the soil when the soil temperature is between 50 degrees and 80 degrees F at the injection depth (6 to 8 inches). Do not fumigate when soils are too wet or too cold. Notes: The liquid chemical is under pressure and extremely hazardous. Chloropicrin is the active ingredient in tear gas and is used as a warning agent. It irritates the eyes and upper respiratory tract. All residues must volatilize from the soil prior to planting. Aerate the soil for at least 2 weeks after uncovering the treated area. Under some conditions, the levels of ammonia nitrogen in the soil may be increased. Use nitrate sources of nitrogen fertilizer until plants are well established and soil is above 65 degrees F to avoid ammonia injury. This is a restricted use product. | ||
| Vapam, Sectagon (metham) Producer: Zeneca | ||
| Application rate: | 239-318 lb ai/A. | |
| Formulation | per acre | per 1000 sq ft |
| 3.18L | 75-100 gal | 1.7-2.3 gal |
| Other formulations may be available. Carefully read the
labels of other products to determine the rates of application specified for those products.
Stability: Is not volatile but breaks down to methylisothiocyanate, which is rapidly lost through volatility. Mode of action: Breaks down into methylisothiocyanate, which disrupts the growth of most organisms that absorb it. Crop uses: Site preparation for high-value crops primarily in seed or liner beds. Kills weeds, their seeds, and some disease-causing organisms. Weed control strengths: Controls small seeded broadleaved weeds and grasses. Weed control weaknesses: Provides poor control of legumes, sedges from seed, and morningglories. Use recommendations: Soil temperature must be between 45 degrees and 90 degrees F at 3 inches. The seedbed should be prepared prior to application, with adequate moisture for good plant growth for 7 to 14 days before treatment. Germinating weed seeds are more easily controlled than dormant seeds. Use the solution promptly after mixing; do not allow it to stand. Seal the surface as soon after application as possible by compacting, irrigating, or covering with plastic. Activity is increased by the use of a plastic cover. Cultivate 2 inches deep 7 days after treatment to aerate the soil. Do not seed earlier than 21 days after application if a plastic cover is used. Notes: Do not apply within 4 feet of growing plants or closer than the drip line of trees and large shrubs. | ||