Non-specific influence of pH on microbial adaptation and insecticide efficacy in previously-treated field soils

Suett, D.L.; Jukes, A.A.; Parekh, N.R.

Non-specific influence of pH on microbial adaptation and insecticide efficacy in previously-treated field soils

1996

Suett, D.L. | Jukes, A.A. | Parekh, N.R.

The influence of soil pH on the development, stability and expression of accelerated biodegradation of soil-applied insecticides was studied at a single site in four areas, with mean pH values of 5.4, 6.1, 6.3 and 7.5. A brassica crop was treated at sowing with the commercially-recommended dose of carbofuran or chlorfenvinphos. After harvesting this crop the efficacy of a second application of each insecticide was assessed 5 and 14 months after the initial application. Microbiological studies were done to determine the numbers of microorganisms able to degrade carbofuran, carbofuran phenol or chlorfenvinphos as the sole source of carbon. With both insecticides there were significant differences in behaviour, as well as in their biological performance against larvae of the cabbage root fly (Delia radicum) in the different plots. In previously-untreated soils, chlorfenvinphos was similarly and highly effective at all pH values, whereas the performance of carbofuran declined steadily with increasing pH. In the previously-treated soils, the efficacy of chlorfenvinphos was reduced only in the pH 7.5 soil, whereas that of carbofuran was much reduced at all pH values except pH 5.4. Microbiological studies showed that carbofuran and carbofuran phenol-degrading organisms were present in all the previously-treated soils, but that carbofuran phenol-degrading organisms were predominant in the soils with highest pH.

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