RATIONALE A study of pesticide transformation products (TPs) was carried out in soils of agricultural areas working under integrated pest management programs (IPMs). Bupirimate and cyromazine were the pesticides detected in soils after an initial pre‐screening. The aim of this work was the identification of relevant TPs of these two pesticides. METHODS Soil samples were extracted by pressurized liquid extraction (PLE), using a mixture of ethyl acetate/methanol (3:1, v/v), and analyzed by ultra‐high‐pressure liquid chromatography coupled to hybrid quadrupole‐time‐of‐flight mass spectrometry (UHPLC‐QTOF‐MS). For confirmation purposes, tandem mass spectrometry (MS2) experiments were carried out using QTOF‐MS, obtaining specific fragment structures of the pesticides and their degradates. RESULTS Retention times and exact masses of the protonated molecules were used for the identification of the pesticides bupirimate (m/z 317.1642) and cyromazine (m/z 167.1040) and their respective TPs, namely ethirimol (m/z 210.1601) and melamine (m/z 127.0727). A novel strategy using pseudo‐MS3 experiments was developed to confirm the structure of bupirimate TP (ethirimol). This strategy consists of generating the particular TP in the ion source, via collision‐induced fragmentation, and then performing MS/MS to the fragment ion formed in‐source. CONCLUSIONS Ethirimol and melamine were identified as degradation products of bupirimate and cyromazine, respectively. The study was applied to the analysis of 15 agricultural soil samples finding bupirimate and ethirimol in seven samples, cyromazine in one sample and melamine in four samples. Copyright © 2012 John Wiley & Sons, Ltd.