The 1970's saw a dramatic increase in the use of the whole systems approach (plastic

mulch and fumigation). A majority of the tomato producers in Florida began using either plastic

mulch or a combination of plastics and fumigation (Bewick, 1989).

 "The systems approach was developed for tomato production in south Florida, but

 by 1978 it had become an integral part of tomato production in every part of the

 state. By 1978, 81% of tomato fields were mulched and 64% of tomato fields

 were fumigated. Of those fields that were fumigated, 94% were mulched. Six

 soil fumigants most frequently used were: methyl bromide (67% methyl bromide

 + 33% chloropicrin), Vorlex, Vapam, Telone, EDB and DBCP. Of these, the

 first three are broad spectrum, and the last three are more specifically

 nematicides" (Bewick, 1989 p. 66).

Of the six soil fumigants listed, methyl bromide, Vapam and Telone are the only remaining

chemicals currently available.


Methyl Bromide in the Soil

 The chemical reactions of methyl bromide (MB) occurring in the soil are important to

understanding the effectiveness of methyl bromide. As a soil fumigate methyl bromide is

applied as a liquid via tractor drawn chisels or shanks six to eight inches deep in the soil. Due

to its high vapor pressure, it volatilizes rapidly and moves through the soil by mass flow and

then by diffusion (Munnecke and Gundy, 1979). Soil movement of gaseous phase methyl

bromide is specifically affected by soil moisture content. Methyl bromide follows a path of least

resistance. If soil moisture is too low, unobstructed air passages will allow methyl bromide to

rapidly diffuse out of the soil and be lost to the atmosphere. If the soil is too wet, movement