Effect of Fungicides, Benomyl and Thiram on Soil Microflora and Some Inhabitant Fungi

Effects of Benomyl and Thiram on the soil microflora and some soil inhabitant fungi were studied using the_ soil (sandy loam) of the experimental field, Okayama University. Under field conditions, heavy application of Benomyl did not affect significantly the soil microflora. Thiram, however, reduced the fungal population in soil to 1/6 at the next day of treatment, but recovered to the normal level after 6 days. Under laboratory conditions, both fungicides did not affect soil microflora. Population of Benomyl-to lerant fungi was about 1/10 of the total fungi and increased slightly in the field soil by treatment with Benomyl at the later stage of experiment during June to October. Neither Thiram-tolerant fungus nor bacterium was found in both Thiram-treated and non-treated soils. A fungus highly tolerant to Benomyl was isolated and identified as Aspergillus versicolor, and found to not have the metabolic activity to degrade BCM. The absorption of BCM by the mycelia of this tolerant fungus, A. versicolor, was less than half of the BCM-sensitive one, such as Cladosporium harbarum.