Effects of a sequential application of three pesticides on soil microarthropods in a field study

In many crops, pesticides are applied simultaneously or sequentially, exposing soil microarthropods to dynamic residue mixtures. Yet, little is known about the possible ecological effects of such mixtures. This study investigated the effects of three commercial pesticides—clopyralid (herbicide), cypermethrin (insecticide), and pyraclostrobin (fungicide)—applied individually and in sequence on soil microarthropods (Collembola and Acari) in a field setting. Concurrently, standard laboratory tests were conducted to assess the toxicity of the individual pesticide formulations to the reproduction and survival of the Collembola Folsomia candida exposed in the same field soil. In the field, the formulations were applied individually and sequentially at 1× and 10× the recommended dose. Short-term (i.e., 1 week after application) and long-term effects (i.e., 4 weeks after application) on soil microarthropods were evaluated. In the laboratory, concentration-dependent reduction of F. candida survival and reproduction was observed only for pyraclostrobin and cypermethrin, with no-observed effect concentrations of 9.56 and 94.1mg of active substance per kg dry soil, respectively. In the field, no aggravated effects of the sequential mixture were detected compared to the single pesticide applications. No negative short- or long-term effects were detected on Collembola abundance or diversity from any of the pesticides or their sequential mixture. In contrast, short-term exposure to the insecticide alone or in sequential mixtures significantly reduced Acari abundance in the field, though this effect weakened over time, leaving only a non-significant trend in the long term.