Background and Aims <p>Early blight, caused by <i>Alternaria alternata</i>, is a major challenge to tomato production worldwide. Its management relies heavily on chemical fungicides, which raise concerns about resistance, environmental impact, and food safety. This study assessed humic acid, fulvic acid, and folic acid as adjuvants to reduce fungicide use while maintaining disease control and improving plant and soil health.</p> Methods <p>The antifungal efficacy of difenoconazole alone and in combination with humic, fulvic, or folic acids was evaluated in vitro. Moreover, lysimeter-based trials across different soil types were carried out to assess disease severity, plant performance, and soil biological and chemical properties. Difenoconazole residue dynamics in harvested tomato fruits.</p> Results <p>In vitro assays showed that humic acid and folic acid increased difenoconazole efficacy at low concentrations. IC₅₀ decreased from 12.57&#xa0;μg&#xa0;mL⁻¹ for fungicide alone to 4.71&#xa0;μg&#xa0;mL⁻¹ when combined with humic acid. Lysimeter-based experiments across different soils demonstrated that combined applications maintained effective suppression of early blight severity (59–69%) while improving plant growth (up to 25%), photosynthetic pigment, and yield performance, reaching 52.0 in sandy soil, 60.7 in calcareous soil, and 65.3 Tonnes ha⁻¹ in clay soil. Soil analyses revealed increased organic matter, microbial biomass carbon, dehydrogenase activity, and macronutrient availability, indicating improved biological functioning and fertility. In clay soil, humic substances and folic acid accelerated difenoconazole dissipation, reduced residue persistence in tomato fruits, and shortened the pre-harvest interval from 14.0 ± 2.1&#xa0;days for fungicide alone to about 6.5&#xa0;days with folic or fulvic acid. The dissipation half-life (DT₅₀) also decreased from 3.1 ± 0.4&#xa0;days to 1.3 ± 0.5&#xa0;days with folic acid.</p> Conclusion <p>Integrating humic substances or folic acid with difenoconazole offers a viable strategy to reduce chemical input while sustaining disease control, improving soil health, and lowering environmental burden in tomato production. Future work should evaluate field-scale performance across diverse climates, long-term impacts on soil microbial communities, and optimization of application timing and dosage to support precision disease management systems.</p> Highlights <p>• Humics and folic acids enhance difenoconazole efficacy at low doses.</p> <p>• Combined treatments sustained disease control and reduced residues in tomato.</p> <p>• Organic amendments improved tomato growth, physiology, and stress resilience.</p> <p>• Soil fertility and microbial activity increased under combined treatments.</p> <p>• Amendments-fungicides integration supports sustainable disease management.</p>