Distribution, Efficacy, and Off-Tarp Emissions Of Carbonated Fumigants In Low Permeability Film Tarped Field.

Previous research in Florida indicated that carbonated fumigants can distribute more quickly and uniformly through soil which suggests that soil-borne disease control could be improved compared to conventional nitrogen pressurized fumigants. Tarping fields with totally impermeable film (TIF) may further improve exposure of carbonated fumigants by more effectively retaining the fumigant in soil. However, information on the dispersion of carbonated fumigants under low permeability film in California sandy loam soil is limited. A field trial was conducted to determine the distribution, efficacy, and emissions of the carbonated Telone C35 [63.4% 1,3-dichlorpropene (1,3-D) and 34.7% chloropicrin (CP)] under polyethylene (PE), TIF, and in bare soil. The treatments included an untreated control, conventional nitrogen pressurized Telone C35 and under PE, TIF or no film, and carbonated Telone C35 at both full rate and 2/3 rate under TIF or PE. An additional 60 cm tarp extension in the carbonated Telone C35 at 2/3 rate was used with an objective to minimize off-edge emission. Muslin bags containing 100 g of soils infested with citrus nematodes (Tylenchulus semipenetrans Cobb) were buried at 15, 30, 60, and 90 cm below the soil surface in each plot prior to fumigation to determine fumigation efficacy. Results showed that fumigant concentration under TIF were 2-4 times higher to that under PE regardless of carbonation. Both 1,3-D and CP concentrations under film decreased with distance from the shank injection line regardless of film type. At the tarp edge, the 1,3-D concentration was 57-65% lower and the CP concentration was 88-94% lower than that at the shank injection line. Both 1,3-D and CP emissions immediately off TIF edge were detected during the initial fumigation days. With an additional tarp extension, the fumigant emission off tarp edge was dramatically reduced. The buried citrus nematodes were completely controlled throughout the soil profile, especially under TIF. These data suggest that the combination of 2/3 rate carbonated fumigants and TIF tarping could achieve the satisfactory pest control while at least a 60 cm tarp extension should be considered to avoid the fumigant emission off tarp edge.