Fumigation efficacy and emission reduction using low-permeability film in orchard soil fumigation.

BACKGROUND: Many orchards use fumigation to control soilborne pests prior to replanting. Controlling emissions is mandatory to reduce air pollution in California. This research evaluated the effects of plastic film type [polyethylene (PE) or totally impermeable film (TIF)], application rate of Telone C35 [full (610 kg ha(-1) ), 2/3 or 1/3 rates] and carbonation at 207 kPa on fumigant transport (emission and in soil) and efficacy. RESULTS: While increasing fumigant concentrations under the tarp, TIF reduced emissions >95% (∼2% and <1% of total applied 1,3-dichloropropene and chloropicrin respectively) relative to bare soil, compared with ∼30% reduction by PE. All fumigation treatments, regardless of film type, provided good nematode control above 100 cm soil depth; however, nematode survival was high at deeper depths. Weed emergence was mostly affected by tarping and fumigant rate, with no effects from the carbonation. CONCLUSION: TIF can effectively reduce fumigant emissions. Carbonation under the studied conditions did not improve fumigant dispersion and pest control. The 2/3 rate with TIF controlled nematodes as effectively as the full rate in bare soil or under the PE film to 100 cm soil depth. However, control of nematodes in deeper soil remains a challenge for perennial crops.

Effects of CO2 dissolution on phase distribution and degradation of dimethyl disulfide in soils under grape production.

BACKGROUND: Dimethyl disulfide (DMDS) is a fumigant recently registered in parts of the United States. The fumigant has high pesticidal activity, but does not disperse in soils as well as other fumigants. This study assessed the use of CO2 as a propellant to improve soil dispersion and diffusion by evaluating the partitioning and degradation of DMDS after carbonation in four vineyard soils collected in California. RESULTS: The soil with the highest organic carbon content (Clarksburg) had the highest soil-water partition coefficient (Kd ) (P < 0.001), which increased after carbonation. However, DMDS sorption decreased in the Mecca and Fowler soils. Henry's law constant (Kh ), which measures a compound's potential for partitioning between air and water, doubled from 0.04 to 0.10 with the addition of CO2 , indicating less DMDS solubility. Carbonation did not negatively affect DMDS's half-lives in the different soils. CONCLUSION: While trials are needed for validation of field-scale impacts, carbonation had mixed effects on soil partitioning and no discernable impact on degradation, but greatly decreased DMDS water solubility. This indicates that carbonation could improve some facets of DMDS diffusion and dispersion, depending on soil properties (carbon content and moisture), without greatly affecting its other behaviors.