throughout the pores of the soil. However, MITC has a high affinity for the liquid phase;

therefore, the chemical does not move as readily through the soil as does methyl bromide

(Noling, 1991).

 There are several factors that influence the efficacy of Vapam when applied to the soil.

Soil temperature and moisture play an important role in the conversion of metham sodium to

MITC. If the soil temperatures are too high and soil moisture is low, conversion is increased,

and the chemical may diffuse out of the soil too quickly, not allowing for an accumulation of

the chemical in the soil and effective control. If the soils are too wet and temperatures are cool,

the rate of decomposition to MITC is decreased. Under this condition the chemical cannot

accumulate in the soil to levels that are needed for effective control. If temperatures are low

or excessive water is applied after application of the chemical, the MITC may remain in the soils

longer than desired and result in delayed planting (Gerstl et al., 1977).

 Several studies have also shown that soil type influences available MITC. Gerstl et al.

(1977) found that soils high in organic matter or clay incurred a delay in the amount of MITC

available to diffuse throughout the soil. Thus, for effective results, clay soils or soils high in

organic matter can require higher initial concentrations of Vapam.

 For field application, Vapam can be applied using a chisel or an irrigation system. For

application via chisel, it is recommended that soil temperatures at 3 inches in depth are in the

range of 60 to 90 degrees Fahrenheit. Soil moisture should be approximately 50 to 80% of field

capacity. Rates of application need to be adjusted depending on environmental and field

conditions (Noling, 1993d). Vapam has been commonly applied via chisel injection, placed