Chemical Analysis of Southern Pine Pole Stubs Thirty-Nine Months Following Treatment with Three Methylisothiocyanate-Based Fumigants
R J Ziobro, J Fomenko, D J Herdman, J Guzzetta, T Pope
Agricultural fumigants have been commercially used in the United States for over 20 years to control internal decay in utility poles and other wooden structures. Of the four fumigants which are currently used in the remedial treatment of utility poles, three are based on methylisothiocyanate (MITC) as being the principal fungitoxic component. Two of these MITC-based fumigants, liquid metham sodium and granular dazomet, chemically decompose within a utility pole to release methylisothiocyanate. The third MITC-based fumigant consists of 97% methylisothiocyanate in a solid melt form. Laboratory and field studies conducted as part of the Cooperative Pole Research Program at Oregon State University have demonstrated the efficacy of all three MITC-based fumigants. However, studies conducted to date have not evaluated the three fumigants under the same experimental conditions. As a result, a field study of the three commercial MITC-based fumigants was established in June, 2000 in southern pine utility pole sections. At the second inspection conducted 39 months following fumigant treatment, chemical assay borings were removed at various pole heights and depths and analyzed for concentrations of MITC using GCMS. The 39 month results showed that MITC concentrations were greatest at all pole heights and core depths in the pole stubs treated with the 97% MITC product. In addition, similar concentrations of MITC were found in the metham sodium and dazomet treated pole stubs. When compared to the corresponding chemical assay results at 13 months following fumigant treatment, the 39 month results showed a sharp increase in concentrations of MITC in the 97% MITC treated pole stubs and a sharp decrease in MITC concentrations in the metham sodium treated pole stubs. MITC concentrations remained relatively unchanged in the dazomet treated pole stubs from 13 to 39 months following fumigant treatment. When compared to a MITC threshold value for decay fungi proposed by Oregon State University, the chemical assay results at 39 months indicated all three fumigants are effectively protecting the zone of fumigant treatment (15.2 cm below to 15.2 cm above groundline) of southern pine pole stubs. However, the greatest protection within and above the zone of treatment was provided by the 97% MITC treatment. Future sampling and chemical analysis of the southern pine pole stubs are planned to monitor long term efficacy of the fumigant treatments.
Keywords: Methylisothiocyanate, metham sodium, dazomet, southern pine poles, field studies, efficacy