Effects of fenvalerate and permethrin on soil arthropods and on residues in and decomposition of barley straw

The effects of two pyrethroids, fenvalerate and permethrin, were studied in field experiments on two soil types: organic soil and sandy loam. The objectives were to determine 1) the persistence of fenvalerate and permethrin in straw, 2) the effects of the pyrethroids on epigeal Arachnida and Collembola, and other soil animals and 3) the effects of the pyrethroids on the decomposition rate of straw. The residues of fenvalerate and permethrin in straw approximately 2 months after application varied between 0.1 to above 5 mg/kg straw in 1986, 1988 and 1989, but was less than 0.5 mg/kg straw at harvest in 1991. No pesticide residues were found in straw samples taken in the following summer in the 1991 experiment. The decomposition rate of straw did not differ between permethrin and fenvalerate- treated plots and control plots. The rate of decomposition was slightly higher in sandy soil than in organic soil, but the same on tilled and non-tilled plots. Fenvalerate and permethrin affected the numbers of epigeal Arachnida and Collembola in the field. Araneae were more numerous in pitfall samples taken from control plots than in insecticide-treated plots immediately after treatment. In organic soil the difference was marginally significant after harvest. The abundance of Acarina in pitfalls was significantly lower in insecticide-treated plots than in control plots. In the sandy soil experiment, less Collembola occurred in pitfalls of fenvalerate plots than in permethrin or control plots. There were no differences in any of the groups of soil animals in soil cores extracted with dry funnels between the treatments