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Effects of the herbicide dalapon on the soil microflora are evaluated. Measurements were made on populations and pure cultures of micro-organisms, dehydrogenase and phosphatase, soil respiration, and nitrogen transformations. At normal concentrations of 2.6 and 26 ppm, dalapon had little effect and is unlikely to harm the soil microflora or soil fertility. At abnormal concentrations of 266 and 2,660 ppm, marked effects occurred on the microflora and its activities. In one soil, 2,660 ppm dalapon significantly increased production of ammonium-nitrogen; nitrification was almost totally inhibited in this soil. The results are discussed in terms of the validity of the tests for detecting effects of pesticides on the soil microflora. Some problems, particularly of data interpretation and evaluation, are high-lighted.

The production and usage of herbicides have increased dramatically in recent years. Consequently there is growing concern about the effects of these chemicals on the environment, particularly the possible long-term effects on soil fertility which may result from disturbance of the soil microflora. This review considers the recent developments in the study of the interactions between herbicides and microorganisms, and discusses the problems of evaluating the results of such studies with a view to determining or predicting possible short-term or long-term effects which may be of practical significance.

A microbial community isolated from wheat root systems was capable of growth on mecoprop as the sole carbon and energy source. When exposed to fresh herbicide additions, the community was able to shorten the lag phase from 30 days to less than 24 h. The community comprised two Pseudomonas species, an Alcaligenes species, a Flavobacterium species, and Acinetobacter calcoaceticus. None of the pure cultures was capable of growing on mecoprop. Certain combinations of two or more community constituents were required before growth commenced. The mecoprop-degrading community could also degrade 2,4-dichlorophenoxyacetic acid and 2-methyl-4-chlorophenoxyacetic acid but not 2,4,5-trichlorophenoxyacetic acid.