Location: Water Management ResearchTitle: Degradation and adsorption of carbonated dimethyl disulfide in soils with grape production in california Author
Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 10/3/2012
Publication Date: 11/6/2012
Citation: Cabrera, A., Conkle, J., Qin, R., Wang, D., Gan, J. 2012. Degradation and adsorption of carbonated dimethyl disulfide in soils with grape production in california. International Conference on Methyl Bromide Alternatives and Emissions Reductions. 59:1-3. Interpretive Summary: Dimethyl disulfide (DMDS) is a pre-plant soil fumigant that has zero ozone depletion potential. This fumigant can be delivered through shank and drip systems and applied alone or in combination with other fumigants. DMDS is used to control weeds, soil-borne plant pathogens and nematodes and is currently registered in 21 states, with pending registrations in six additional states including CA. A recent study demonstrated that fumigant diffusion can be enhanced by pressurizing polar fumigants with polar compounds producing a polar-polar interaction. The polar CO2 can be used as a gas carrier and a propellant. However, little is known about what occurs with DMDS in the soil after the addition of CO2. It is unknown whether a faster or slower degradation process occurs or if adsorption to soil is affected when CO2 is used as a gas carrier. In this laboratory study two field soils with grape production in CA were tested for degradation and adsorption with or without CO2 carbonation. Preliminary results indicated that CO2 carbonation did not affect DMDS degradation or adsorption. Therefore, the carbonation of DMDS can be expected to last and be available for pest control similar as non-carbonated DMDS. Efficacy studies with carbonated DMDS against nematodes, pathogens and weeds will also be performed.
Technical Abstract: The common method to apply pre-plant soil fumigants is through pressurizing the pesticides with compressed nitrogen gas. However, it is believed that fumigants with relatively low vapor pressure, such as dimethyl disulfide or DMDS, can be better dispersed in soil when applied using CO2 gas. A laboratory study was conducted to investigate the degradation and adsorption of CO2 carbonated verses non-carbonated DMDS in soils. Soils were collected from two vineyards in California. The first soil was a Delhi loamy sand (total organic carbon 0.06%) from a raisin grape production in Fowler, central CA. The second soil was a Carsitas gravelly sand (total organic carbon 0.20%) from a table grape production in Mecca, south CA. The soils were incubated at 10, 24 or 37°C. Triplicate sets of samples from each temperature were evaluated after 0, 1, 7, 21, 28 & 35 days after DMDS application. Extraction of DMDS from soil was performed with ethyl acetate and anhydrous sodium sulfate. Quantification of DMDS was performed with a GC-MS. The half-life of carbonated and non-carbonated DMDS was determined using first-order kinetics. For adsorption determination, 10.62 mg of carbonated or noncarbonated DMDS were applied to each vial, including vials with only water, and equilibrated for 24 h at 10, 24 or 37°C. Adsorption coefficient or Kd was calculated as ratio of adsorbed over water concentrations for respective temperature settings. Additionally, Kd was investigated in the Delhi loamy sand soil using increasing DMDS dosages at 24°C. Preliminary results showed that carbonation did not affect DMDS degradation in soil. In the Delhi loamy sand soil the DMDS half-life ranged from 14 to 35 days depending on the temperature. In Carsitas gravelly sand soil DMDS half-life ranged from 13 to 30 days. The lowest temperature evaluated (10°C) had the slowest degradation rate, thus having the largest half-life days. The adsorption of DMDS was also not affected by the carbonation process. In the Delhi loamy sand soil the Kd ranged from 0.96 to 1 (g/cm3). In Carsitas gravelly sand soil the Kd ranged from 0.88 to 2.01 (g/cm3). Thus, carbonation, temperature, and dose, did not affect DMDS adsorption. The laboratory tests indicated that carbonation did not affect DMDS half-life in two different grape growing soils of CA. Temperature appeared to be the most important factor affecting DMDS degradation, where higher temperatures favor the degradation process. The adsorption of DMDS was also not affected by carbonation, temperature and dose. Therefore, the carbonation of DMDS can be expected to last and be available similarly as non-carbonated. This will be essential for a lasting efficacy when low carbonated rates are applied for pest control.