Formulation type and active substance show limited influence on dislodgeable foliar residues in a small-scale greenhouse study on soybean

Abstract A small-scale dislodgeable foliar residue study under controlled greenhouse conditions assessed the influence of formulation type and physicochemical properties of active substances on normalized residues immediately after the spray deposits had dried. Five active substances (deltamethrin, spirotetramat, thiacloprid, tebuconazole, and trifloxystrobin) were tested across 5 formulation types, representing 11 commercial products applied to soybean plants. Statistical analysis revealed no significant differences in normalized residues among formulation types for tebuconazole, spirotetramat, and thiacloprid. For deltamethrin, only water-dispersible granules versus oil dispersion differed significantly, while for trifloxystrobin only water-dispersible granules versus emulsifiable concentrate differed. All other pairwise comparisons were non-significant, indicating limited influence of formulation type. Physicochemical parameters of the active substances tested (water solubility 0.00027–184 mg/L; logarithmic octanol–water partition coefficient 1.4–6.4; molecular weight 253–505 g/mol) showed no apparent correlation with normalized residues. Four of 5 active substances clustered around a common mean of 0.71 µg/cm 2 per kg active substance applied per hectare (64–123% relative to this mean, excluding 2 outlier formulations). Deltamethrin showed lower values, potentially reflecting its extreme physicochemical properties and substantially lower application rates. A supplementary dislodgeability experiment with spirotetramat and thiacloprid showed near-complete residue removal (92.6–108.5%) using 2 consecutive extractions, supporting the dislodging protocol’s effectiveness for the active substances and formulations tested. Under the conditions tested, formulation type and active-substance physicochemical properties showed limited influence on normalized residues. Confirmation across additional crops, growth stages and wider physicochemical ranges is needed before broader conclusions can be drawn.