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Title: INCOMPATIBILITY OF METAM SODIUM WITH HALOGENATED FUMIGANTS

Author
item GUO, MINGXIN - UC RIVERSIDE, CA
item Yates, Scott
item Schneider, Sharon
item ZHENG, WEI - UC RIVERSIDE, CA

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2004
Publication Date: 11/22/2004
Citation: Guo, M., Yates, S.R., Papiernik, S.K., Zheng, W. 2004. Incompatibility of metam sodium with halogenated fumigants. Pest Management Science. 61:467-476.

Interpretive Summary: Metam sodium is used extensively to control weeds, nematodes and pathogenic fungi in economically important turf, fruit and vegetable production. In moist soil, metam decomposes rapidly to volatile methyl isothiocyanate (MITC). To improve the control of all major classes of plant pathogens (i.e., weeds, nematodes and fungi), researchers have contemplated using formations of MITC and 1,3-D and CP. However, simultaneous or combined applications of metam with these halogenated fumigants via drip irrigation systems did not show the expected synergism, and yields of strawberry were significantly lower than treatments spiked with these fumigants individually. However, a sequential application of metam by water dripping two weeks following shank injection of CP or Telone C-35 provided equivalent sterilization effect as standard fumigation with MeBr/CP. This suggests that some interaction occurs when metam is mixed with 1,3-D and CP in aqueous solution. In a column study, we noticed that soil-gas concentrations of fumigants were 10 to 100 times lower than the reported and model calculated when Vapam (42 percent of metam sodium) was simultaneously applied to the soil with 1,3-D and CP by either direct injection or drip application. Further studies demonstrated that metam reacted rapidly with a variety of halogenated fumigants in moist soil, water, and even polar organic solvents. The objectives of this study were to investigate the incompatibility of metam with halogenated fumigants and to examine the facilitated transformation of 1,3-D, CP, MeBr and other potential MeBr alternatives at the presence of metam. The result will provide guidance for fumigant application strategies in practice.

Technical Abstract: Combined application of different fumigants is a common practice to treat soil for a broad-spectrum pest control, and simultaneous usage of currently available fumigants 1,3-dichloropropene (1,3-D), chloropicrin (CP) and methyl isothiocyanate (MITC) is intended to obtain synergic pesticidal effects. As a precursor of MITC, metam sodium (metam) is used widely in soil fumigation. In this study, the compatibility of metam with halogenated fumigants 1,3-D, CP, MeBr, methyl iodide (MeI) and propargyl bromide (PgBr) was tested. Decomposition of the halogenated fumigants in moist soil, water, and organic solvents was examined at the presence of metam. Metam was incompatible with halogenated fumigants in all three media, experiencing chemical reactions with the latter at a high rate. At approximately 1:100 molar ratio of halide:metam in acetonitrile, all test halogenated fumigants disappeared within 1 h. In water at 1:15 halide:metam ratio, more than 50 percent of the applied halogenated fumigants were degraded by metam within 7 h. In moist soil, 15-95 percent of the halogenated fumigants were decomposed via reacting with metam in 72 h at 1:1 molar ratio. Metam reacted so rapidly with CP in 10 percent moisture soil that more than 55 percent of the applied CP was degraded in 4 h at 1:1 molar ratio. Direct-injection or drip-application of Telone C-35 (a mixture of 60.5 percent 1,3-D and 33.3 percent CP) at 265 mg kg-1 together with Vapam (42 percent metam) at 585 mg kg-1 resulted in disappearance of 100 percent of the applied CP and 18-35 percent of 1,3-D in 8 h. Simultaneous application of halogenated fumigants and metam will yield poor pest-control effect and should be avoided in practice.