Off-tarp emissions, distribution, and efficacy of carbonated fumigants in a low permeability film tarped field

Authors: QIN, RUIJUN - Oregon State University; Gao, Suduan; THOMAS, JOHN - University Of Florida; Wang, Dong; HANSON, BRADLEY - University Of California

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2017
Publication Date: 6/10/2017
Citation: Qin, R., Gao, S., Thomas, J.E., Wang, D., Hanson, B.D. 2017. Off-tarp emissions, distribution, and efficacy of carbonated fumigants in a low permeability film tarped field. Science of the Total Environment. 603-604:1-7. doi: 10.1016/j.scitotenv.2017.06.001.
DOI: https://doi.org/10.1016/j.scitotenv.2017.06.001

Interpretive Summary: Pre-plant soil fumigation is a disinfestation strategy used commonly to control soil-borne pests for the establishment of new orchards. Efficient delivery of fumigants to the rooting zone and control of emissions are important tasks to achieve in soil fumigation. This research investigated effects of carbonation (dissolving carbon dioxide into fumigants) and totally impermeable film (TIF) with and without tarp extensions on fumigant transport. Results show that carbonation with 1.5% of dissolved carbon dioxide was not sufficient to improve fumigant dispersion significantly in soil. However, off the tarp emissions were generally very low and an extension of 60 cm tarp can reduce emissions of 1,3-dichloropropene by an additional 70% or more. This research confirmed that a 2/3 fumigant rate under TIF provided nematode control that was equal to the full rate. The research identified a need for a higher amount or pressure of carbonation to improve fumigant dispersion in soil, but there may be challenges in achieving this condition when operating under field conditions.

Technical Abstract: Carbonated fumigants have been shown to distribute quickly and uniformly in sandy soils and improve pest control efficacy for annual crops. Low permeability films, such as VaporSafe® (TIF), could further improve fumigant dispersion by effectively retaining the fumigant in soil; however, there is a concern that the TIF can lead to higher off-tarp edge emissions. An orchard field trial was conducted to determine the off-tarp emissions, distribution, efficacy, and fate of carbonated Telone® C35 [63.4% 1,3-dichloropropene (1,3-D), 34.7% chloropicrin (CP)] that was shank-injected at 46 cm soil depth. Treatments included carbonated fumigants at full or 2/3 rates and a full rate of regular (nitrogen-pressurized) fumigants covered with standard polyethylene (PE) film, TIF, or no surface seal. Fumigant emissions at the regular tarp edge (25 cm from the shank line) peaked at 3.98 µg m-2 s-1 for 1,3-D and 0.05 µg m-2 s-1 for CP. The addition of a TIF tarp extension (to 85 cm from the shank line) reduce peak off-tarp emissions to <1 and < 0.03 µg m-2 s-1 for 1,3-D and CP, respectively. Fumigant concentration under TIF was usually at least twice that under PE regardless of carbonation. Carbonation at 345 KPa with 1.5% of dissolved CO2 did not significantly improve fumigant dispersion in soil profile compared to the conventional nitrogen pressurization. In a citrus nematode bioassay, only the 2/3 rate of carbonated fumigation treatment sealed with PE failed to control nematodes at 25 cm away from shank line. This research indicates that a 60-cm TIF extension can effectively reduce off-tarp edge emissions in strip fumigation treatments. While the adaptability of carbonation of fumigants is still questionable, further research efforts are needed in finding effective solutions to control plant parasitic nematodes, which remain a challenge in orchard fumigation.