1. Soil Fumigation Category E Turf and Ornamentals
Pesticide Applicator Training Manual Chapter 12

2. Terms Soil tilth—the degree to which a soil has been tilled.
Mycorrhizal fungi —beneficial microorganisms that transport minerals to the roots of plants and which can be killed by soil fumigation.
Category E--- Chapter 12 Soil Fumigation

3. Introduction
Soil fumigants—volatile chemicals that, when injected into the soil, emit toxic fumes which penetrate the air spaces in sufficient concentration to kill living organisms.
Soil fumigants are extremely toxic and must not be inhaled.
Fumigants are broad spectrum biocides and kill most fungi, soil insects, nematodes, and weeds.
Fumigants will not kill most of the soil resident bacterial diseases or viruses.
Methyl bromide is the most important soil fumigant. It is used for high value crops such as tomatoes, peppers, strawberries, seed potatoes, and several ornamentals.
Methyl bromide is also highly destructive to atmospheric ozone.
Methyl bromide usage is being phased out under international treaty (1991 Montreal Protocol). Florida estimates 61-63% reduction in tomato and pepper production unless alternatives to methyl bromide can be found.
Metam-sodium is the active ingredient in several products lines including Vapam®, Busan®, Nemasol®, and Metam® products.

4. Soil Fumigation Credit: University of California, Davis
Verticillium wilt fungus (Verticillium dahliae) can persist in the soil for up to 20 years unless fumigation is used.
Credit: Smithsonian Magazine
December 1996

5. Successful Soil Fumigation
Goals:
Safe and accurate application.
Rapid dissipation after completion.
Factors in successful fumigation:
Soil temperature between 60-80°F at 6 inch depth.
Soil moisture between 50-75% capacity.
Good soil tilth.
Proper selection of fumigant for the soil type.
Organic mater must be decomposed.
Seals—usually plastic tarps to prevent too-rapid escape of the fumigant.
Best time to apply—late summer or early fall.
Waiting period before planting—range 2 weeks to 2 months.
Temperature—if too low the material will volatilize too slowly and may cause phytotoxicity—if temperature is too high the fumigant will volatilize too rapidly for effective control.
Moisture—if soil is too wet the spread of gases will be too slow—if too dry the volatilization will be too fast.
Tilth—large clods of soil will result in the gas leaving the soil too rapidly.
Soil type—amount and type of organic matter will influence the amount of fumigant required—muck soil require 2x the amount of fumigant required by lighter soils.
Seals— lower volatility fumigants can be sealed with surface watering.

6. Soil Fumigation Special Considerations
Temporary reduction of nitrifying bacteria in soil—can result in buildup of ammonium levels that could damage early crops.
Reduction of pests and predators.
Potential pest ‘rebound.’
Mycorrhizal fungi will be killed—will take time to recolonize.