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NC State Extension

Lecture 3: Fumigation

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  • Fumigants kill weed seeds and vegetative propagules
  • Fumigants are TOXIC
  • For all fumigants: site preparation is critical to product performance

Fumigants available

  • Metham Sodium (liquid)
  • Basamid (granules)
  • Steam

For Best Results Soil Should Be:

  • Cultivated to 8 inches
  • Free of plant debris and clods
  • 55 F at 6 inches
  • Moist, Not wet
  • Amended before fumigation

Methyl bromide

  • The quickest, most versatile & effective
  • No longer available

Metham sodium (formerly Vapam)

  • Liquid application
  • Tarp helps but can be “sealed” with irrigation
  • Time: 7 days, then shallow cultivate, then wait another 7 to 14 days

Basamid (dazomet)

  • Granular application
  • Rototill, then seal surface & irrigate
  • Time: 7 days, then shallow cultivate, then wait another 7 to 14 days

For best results with Metham or Basamid

  • Use a tarp
  • If not, keep soil surface moist for 7 days. (This seals the surface and traps the vapors)

Steam Pasteurization

The soil should be maintained at 180oF for a minimum of 30 minutes. This treatment is sufficient to kill most pathogenic organisms; however, many weed seeds will escape .


Similar to pasteurization but using solar energy to heat the soil in order to kill pathogens, arthropods and weeds. Cover the soil with CLEAR plastic during the summer. Preferably elevate the plastic to trap more heat. This works well in regions that have high solar irradiance but not as well in NC. Small-seeded weeds (such as chickweed and henbit) can be suppressed but perennial weeds (like bermudagrass and nutsedge) and large-seeded weeds (like morningglory and smartweed) are generally not well controlled.

Common reasons fumigants don’t work

  • Soil too wet or too dry
  • Soil too cold
  • Heavy soils not cultivated to adequate depth
  • Some hard-seeded weeds are not controlled (clover, Car. geranium)


Prevent the introduction of weed propagules
Top soil, organic amendments, weeds in adjacent property, balled and burlapped plants

Study Questions:

  1. Compare and contrast how the mode of action of fumigants differs from that of preemergence herbicides.
  2. List the 3 main chemical fumigants. Compare and contrast them with regards to how rapidly they work, covered / not covered/ toxicity / formulation / how they are applied
  3. Compare and contrast steam pasteurization and solarization.
  4. Describe the site preparation necessary to achieve maximum benefit from a soil fumigation.
  5. What are the common reasons why soil fumigation may not work.
  6. What types of weeds would likely be controlled by soil solarization in NC?
  7. What types of weeds would likely NOT be controlled by soil solarization in NC?
  8. List 2 weeds that would likely not be controlled by Methyl Bromide fumigation.
  9. When will Methyl Bromide no longer be available?