Legacy hexaconazole and tricyclazole residues hinder organic transition in paddy rice cultivation

Abstract

Legacy pesticide contamination poses a critical barrier to organic certification of conventional rice farms. This 3‐year study (2021–2023) investigated hexaconazole and tricyclazole persistence in paddy soil, water, rice aboveground biomass (AGB), and grain following foliar application of a premixed formulation to rice ( Oryza sativa subsp. japonica ). Double‐exponential modeling revealed biphasic dissipation patterns for both fungicides: rapid initial decline followed by a dominant slow phase (>99%). Rice grain residues remained below maximum residue limits throughout the study; however, hexaconazole in AGB exceeded the animal feed limit (0.01 mg kg −1 ) at the 2021 harvest. Both fungicides persisted in soil across all three growing seasons, while paddy water residues declined below quantification limits by the third year. These findings indicate that the current mandatory 2‐year organic transitional period may be insufficient for farms with a history of hexaconazole and tricyclazole use, warranting extended conversion periods and compound‐specific regulatory reassessment.