Persistence and Dissipation Pattern of Azoxystrobin and Difenoconazole in Turmeric (Curcuma longa L.)

Turmeric (Curcuma longa L.) is a major spice crop in India, where foliar diseases such as leaf blotch (Taphrina maculans) and leaf spot (Colletotrichum capsici) cause substantial yield losses. A ready-mix formulation of azoxystrobin (18.2%) and difenoconazole (11.4%) is effective against these diseases, but no residue data are available for the agro-climatic conditions of South Gujarat. This two-year field study investigated the persistence, dissipation kinetics, and harvest-time residues of both fungicides in turmeric leaves, soil, and rhizomes using a validated QuEChERS-based LC-MS/MS method. First-order kinetics adequately described dissipation, with alternative models (FODE and Higuchi) showing no statistically significant improvement. Azoxystrobin half-lives (DT₅₀) ranged from 13.1-14.3 days in leaves and 21.5-21.6 days in soil, while difenoconazole exhibited DT₅₀ values of 11.9-12.2 days in leaves and 24.5-25.9 days in soil. The slower soil dissipation of difenoconazole (2.1× longer than in leaves) compared to azoxystrobin (1.6×) is attributed to its higher lipophilicity (log K _ow 4.4 vs 2.5) and stronger sorption to soil organic carbon (K _oc 1660-7740 vs 399-1094 mL g^-1). Residues in turmeric rhizomes at harvest were below the limits of quantification (0.010 mg kg^-1 for azoxystrobin; 0.005 mg kg^-1 for difenoconazole) at both recommended and double doses, yielding safety margins exceeding 800-fold relative to established maximum residue limits (8.0 and 4.0 mg kg^-1, respectively). The extended interval between the last spray and harvest (120-180 days) ensured complete dissipation before rhizome maturity. These findings provide the first baseline residue data for this fungicide combination in turmeric and confirm its safe use under the warm, humid, high-rainfall conditions of South Gujarat.