Seven genera plant–parasitic nematodes, i.e. Criconemella sp., Ditylenchus spp., Helicotylenchus spp., Meloidogyne spp., Pratylenchus spp, Rotylenchulus spp. and Tylenchorhynchus were recorded in the rihzospher in tomato plants. Such genera differed greatly in their prevalence and levels of abundance. The genera of Helicotylenchus spp., Pratylenchus sp. and, Meloidogyne spp. were dominant. The genera Tylenchorhynchus sp., Rotylenchulus spp., Criconemella sp. and Ditylenchus spp. were the second most important genera. On the other hand, the genera of Meloidogyne spp. and Tylenchorhynchus sp. were the most frequently occurred. Regarding Peach orchards, there were nine genera plant–parasitic nematode, i.e. Criconemella sp., Ditylenchus spp., Helicotylenchus spp., Hemicriconemoides sp. Heterodera spp., Meloidogyne spp., Pratylenchus spp., Rotylenchulus spp. and Tylenchorhynchus spp. The genera Helicotylenchus spp. and Hemicriconemoides sp. were dominant. Genera, however Pratylenchus spp .and Meloidogyne spp. were the most frequently occurred. The environmental behavior of the nematicide residues, fothiazate in sandy loam soils in peach orchards and tomatoe plants were investigated under field conditions. In relation to the degradation pattern in the selected soils, the obtained results indicated that the nematicide residues were dissipated more rapidly in the soil planted with tomatoes compared with peach orchard soils.  The calculated half-life periods (t1/2) were 3.7 and 7.4 days for fosthiazate in soil planted with tomatoes and trees of peach.