Two ®eld experiments were done in which plots of oilseed rape, immediately adjacent to the ®eld margin, were left untreated or treated with the slug-parasitic rhabditid nematode Phasmarhabditis hermaphrodita. Nematodes were applied at a rate of 3 Â 10 9 ha À1 . Slug populations within plots were low and nematode application had little detectable effect on slug numbers, biomass or slug damage to the crop. There was a large snail community in the ®eld margin in both experiments, but P hermaphrodita had no detectable effect on the abundance of any of the nine snail species recorded. The susceptibility of seven common hedgerow species (Monacha cantiana, Cepaea hortensis, Cepaea nemoralis, Pomatias elegans, Oxychilus helveticus, Clausilia bidentata and Discus rotundatus) to P hermaphrodita was tested in the laboratory. Snails were kept con®ned for three weeks on soil without nematodes, or with P hermaphrodita applied at the recommended application rate or ®ve times this rate. Soil treatment with the recommended rate of nematodes caused signi®cant mortality only for the snail M cantiana and the susceptible slug Deroceras reticulatum. Soil treatment with ®ve times the recommended rate caused signi®cant mortality of the slug D reticulatum and the snails M cantiana and C hortensis, but not any other species. Reasons why application of P. hermaphrodita to arable crops in Britain is unlikely to pose a substantial threat to non-target molluscs are discussed.

The repeated use of a given pesticide may induce a selection of the soil microbial population, resulting in a rapid degradation of the respective xenobiotic. Patterns of atrazine degradation (mineralization, formation of metabolites and nonextractable residues (NER)) were evaluated in two Brazilian soils with a history of atrazine application. Results were compared with those obtained from soils that had no agricultural use or herbicide application history. (14)C-Atrazine mineralization in unsaturated treated soils was high. By the 85th day of incubation, 82% of the applied (14)C-atrazine was mineralized in the Rhodic Hapludox and 74% in the Xanthic Haplustox. Mineralization remained low in nontreated soils (

To assess the potential occurrence of accelerated herbicide degradation in soils, the mineralization and persistence of 14 C-labeled and non-labeled atrazine was evaluated over three months in two soils from Belgium (BS: atrazine treated 1973 BC: non-treated) and two soils from Germany (CK: atrazine treated 1986-1989; CM: non-treated). Prior to the experiment, accelerated solvent extraction of bulk field soils revealed atrazine (8.3 and 15.2 µg kg −1 in BS and CK soil), and a number of metabolites directly after field sampling, even in BC and CM soils without previous atrazine treatment, by means of LC-MS/MS analyses. For atrazine degradation studies, all soils were incubated under different moisture conditions (50% maximum soil water holding capacity -WHC max -/slurried conditions).At the end of the incubation, the 14 C-atrazine mineralization was high in BS soil (81% and 83%), and also unexpectedly high in BC soil (40% and 81%), at 50% WHC max and slurried conditions, respectively. In CK soil, the 14 C-atrazine mineralization was higher (10% and 6%) than in CM soil (4.7% and 2.7%), but was not stimulated by slurried conditions. The results revealed that atrazine application history dramatically influences its degradation and mineralization. For the incubation period, the amount of extractable atrazine, composed of residues from freshly applied atrazine and residues from former field applications, remained significantly greater (statistical significance = 99.5% and 99.95%) for BS and CK soils, respectively, than the amount of extractable atrazine in the bulk field soils. This suggests that i) mostly freshly applied atrazine is accessible for a complex microbial community, ii) the applied atrazine is not completely mineralized and remains extractable even in adapted soils, and iii) the microbial atrazine-mineralizing capacity strongly depends on atrazine application history and appears to be conserved on long time scales after the last application.

SummaryThe effects of soil cultivation immediately after application of the rhabditid nematode, Phasmarhabditis hermaphrodita, to the soil surface were investigated in two field experiments. The first experiment was done in mini‐plots separated by barriers, with an artificially introduced population of slugs (Deroceras reticulatum). Nematodes were applied as a drench at a rate of 3 times 109 ha‐1 in one of two application volumes and then left undisturbed or incorporated into the soil by cultivation to 2 cm or 10 cm depth. Moist soil conditions were maintained by irrigation throughout the experiment. Nematode application significantly reduced slug damage to Chinese cabbage seedlings throughout the 7 wk duration of the experiment and the population of D. reticulatum in soil 7 wk after treatment. However, soil cultivation had no effect and did not interact with the effect of nematodes. In the second experiment, in a crop of winter wheat, nematodes were applied to soil by hand‐lance at a rate of 3 times 109 ha‐1 and left undisturbed on the soil surface or incorporated by spring‐tine cultivation to a depth of 2, 5 or 10 cm. In this experiment, nematodes were applied to dry soil. Cultivation alone had no effect. Nematode application reduced slug damage to wheat plants in plots where nematodes were incorporated into the soil, but not where they were left on the surface. There was no detectable impact of nematodes on slug populations in the wheat experiment.

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