Changes in Soil Microflora Following Application of Fungicides Dyrene and Maneb to Tropical Soils

Abstract

Changes in soil microorganisms following applications of 2,4-dichloro- 6-(o-cloroaniline)-s-triazine (Dyrene) and manganese ethylene bisdithiocarbamate (Maneb) at 0, 60, 240, and 960 ppm to the acid lateritic Humatas clay and the alkaline fertile San Anton loam incubated at 23° ± 1°C were studied for 18 months in the laboratory. In general, bacterial numbers increased and actinomycetes and fungi decreased especially at higher concentrations of the chemicals. The bacterial increase disappeared at the 10-month count but persisted longer at the 960 ppm rate of Maneb. Bacteria seem to be the principal microorganisms responsible for degradation of these fungicides in the soil. Maneb caused qualitative as well as quantitative changes in the fungal population. Microorganisms in the two soils differed in their response to the chemical treatment. Inhibition of the microorganisms was offset by inoculation with fresh soil.