The effect of fonofos and carbofuran on microbiological population, and persistence of fonofos in four organic soils infested with onion maggot.

One hundred days after field-application of fonofos as bands under the onion seed, 39 to 59% of that material was present in 3 moderately humified organic soils of pH varying from 5.4 to 6.7. In a low humified organic soil, only 21 to 24% of the applied fonofos remained. Thus humus enhanced the persistence of fonofos and curtailed the stimulating effect of fonofos on soil microbial populations. An assessment of low damage caused by onion maggot was found in a poorly humified soil with an even higher natural infestation than in a moderately humified soil. The effects of fonofos in other soils and of the low rate of carbofuran applied to four different types of soils on the numbers of fungi, bacteria, and actinomycetes were difficult to assess.