ARS | Publication request: Predicting methyl iodide emission, soil concentration, and pest control in a two-dimensional chamber system

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 12, 2010
Publication Date: January 1, 2011
Citation: Luo, L., Yates, S.R., Ashworth, D.J. 2011. Predicting methyl iodide emission, soil concentration, and pest control in a two-dimensional chamber system. Journal of Environmental Quality. 40(1):109-117.

Interpretive Summary: Due to ever increasing state and federal regulations, the future use of fumigants is predicted on negative environmental impacts while offering sufficient pest control efficacy. To foster the development of the best management practice (BMP), an integrated tool is needed to simultaneously predict fumigant movement and pest control without having to conduct elaborate and costly experiments. The objective of this study was to 1) present a 2-D mathematical model to describe both fumigant movement and pest control and 2) evaluate the model by comparing the simulated and observed results. Both analytical and numerical methods were used to predict fumigant transport and fate. To predict pest control efficacy, the concentration-time index (CT) was defined and a 2-parameter logistic survival model was used. Dose-response curves were experimentally determined for methyl iodide (MeI) against three types of pests (barnyardgrass seed [Echinochloa crus-galli], citrus nematode [Tylenchulus semipenetrans], and fungi [Fusarium oxysporum]). Methyl iodide transport and pest control measurements collected from a 2-D experimental system (60 x 60 cm) were used to test the model. MeI volatilization rates and soil gas-phase concentrations over time were accurately simulated by the model. The mass balance analysis indicates that the fraction of MeI degrading in the soil was underdetermined when determined by the appearance of iodide concentration. The experimental results showed that after 24-h MeI fumigation in the 2-D soil chamber, fungal population was not suppressed; more than 90% of citrus nematodes were killed; and barnyardgrass seeds within 20-cm distance from the center were affected. The experimental results were consistent with the predicted results and the model accurately estimated the MeI movement and control. With further development, this approach could be a powerful tool to help growers and fumigant applicators to introduce new and improved fumigation methods into their operations without conducting elaborate and costly experiments. The research would also be of value to the regulatory community and provide a means for rapid evaluation of new fumigation methodology.

Technical Abstract: Due to ever increasing state and federal regulations, the future use of fumigants is predicted on negative environmental impacts while offering sufficient pest control efficacy. To foster the development of the best management practice (BMP), an integrated tool is needed to simultaneously predict fumigant movement and pest control without having to conduct elaborate and costly experiments. The objective of this study was to 1) present a 2-D mathematical model to describe both fumigant movement and pest control and 2) evaluate the model by comparing the simulated and observed results. Both analytical and numerical methods were used to predict fumigant transport and fate. To predict pest control efficacy, the concentration-time index (CT) was defined and a 2-parameter logistic survival model was used. Dose-response curves were experimentally determined for methyl iodide (MeI) against three types of pests (barnyardgrass seed [Echinochloa crus-galli], citrus nematode [Tylenchulus semipenetrans], and fungi [Fusarium oxysporum]). Methyl iodide transport and pest control measurements collected from a 2-D experimental system (60 x 60 cm) were used to test the model. MeI volatilization rates and soil gas-phase concentrations over time were accurately simulated by the model. The mass balance analysis indicates that the fraction of MeI degrading in the soil was underdetermined when determined by the appearance of iodide concentration. The experimental results showed that after 24-h MeI fumigation in the 2-D soil chamber, fungal population was not suppressed; more than 90% of citrus nematodes were killed; and barnyardgrass seeds within 20-cm distance from the center were affected. These experimental results were consistent with the predicted results. The model accurately estimated the MeI movement and control on various pests and can be a powerful tool to evaluate the different pesticides in terms of their negative environmental impacts and pest control under various environmental conditions and application methods.