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Raised beds are used to produce some high-value annual fruit and vegetable crops such as strawberry in California (CA) and tomato in Florida (FL), USA. Pre-plant soil fumigation is an important tool to control soil-borne pests in the raised beds. However, fumigant emissions have detrimental environmental consequences. Field trials were conducted to evaluate emissions of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) in two different production systems with raised beds covered by different tarps. In the CA trial, InLine (60.8% 1,3-D and 33.3% CP) was drip-applied at 340 kg ha(-1) to 5 cm deep in the beds (30 cm high and 107 cm wide) tarped with polyethylene (PE) or virtually impermeable film (VIF). In the FL trial, carbonated Telone C35 (63.4% 1,3-D and 34.7% CP) was shank-applied at 151 kg ha(-1) to 20 cm deep in the beds (22 cm high and 76 cm wide) tarped with totally impermeable film (TIF). Emissions from tarped beds relative to furrows were contrary between the two trials. For the CA trial, the emission was 47% of applied 1,3-D and 27% of applied CP from PE tarped beds and 31% of applied 1,3-D and 15% of applied CP from VIF tarped beds, while that from uncovered furrows was

Methyl bromide controls three major problems in crop production: weeds, nematodes and phytopathogenic fungi. An alternative system was investigated that used various colored plastic mulches with Telone C35 (63.4% 1,3-dichlropropene, 34.7% chloropicrin, 1.9% inert ingredients). This alternative to methyl bromide was to investigate: 1) control weeds through wavelength selective plastic mulches, 2) control fungi by chloropicrin, and 3) control weeds and nematodes by 1,3-dichloropropene. These mulches control weeds by a thickness that prevented weed penetration, especially nutsedges, by retaining phytotoxic fumigant longer, or by allowing infra-red and red light to penetrate through the film while restricting other photo synthetically active wavelengths. Infra-red and red light changed the morphology of nutsedges from a hard plastic-penetrating point to a soft leafy structure that cannot tear the film. The mulches tested were blue virtually impermeable film (VIF), black VIF, black polyethylene film (PE), as well as blue, green, olive, brown, and metalized PE. Conclusions after a two-year study were: 1) that there was no direct correlation between the amount of light transmitted through colored mulch with tomato yield per plant, 2) that the use of fumigation with plastic mulches led to an average increase of 40% in crop yield compared to non-fumigated beds, and 3) finally, that if the grower decided not to use any pesticide, fungicide, or herbicide, then metalized PE mulch would maximize weed control and crop yield.

Methyl bromide, a pre-emergent soil fumigant, is scheduled to be phased out in the US by 2005, with exceptions for critical use. Comparison of some of the physical constants related to distribution and retention for methyl bromide (MBr) to other fumigants yields a useful quantification of possible alternatives. In this study, the atmospheric and subsurface dissipation of methyl bromide as well as (Z)- and (E)-1,3-dichloropropene (1,3-D) isomers in Telone II were examined. The Henry's law constants of the three chemicals at soil temperature and their mass transfer coefficients for movement through an agricultural mulch of UV-resistant, high-density polyethylene (PE) were evaluated using field data. At the soil temperature of 16.4 degrees C, calculated Henry's law constant gave a fumigant ranking of MBr (0.21)(Z)-1,3-D (0.041)(E)-1,3-D (0.027). Since rapid subsurface distribution of a fumigant is highly dependent on the amount in the gas phase, the greater value for Henry's law constant implies faster distribution throughout the soil. After distribution through the soil, retention of the fumigant becomes imperative. Calculation of the fumigant's mass transfer coefficients through PE from field data gave a ranking of the three chemicals: MBr (1.08 cm/h)(E)-1,3-D (3.25 cm/h)(Z)-1,3-D (4.13 cm/h). With mass transfer coefficients of this magnitude, it was concluded that PE film was an inadequate barrier for retaining these fumigants in an agricultural setting.