In Vitro and Field Effectiveness of the Combination of Four Trichoderma spp. Against Sclerotinia sclerotiorum and Its Impact on Potato (Solanum tuberosum L.) Crop Production

White mold (<i>Sclerotinia sclerotiorum</i>) reduces potato yield and quality in Sinaloa, Mexico. This study first evaluated the in vitro efficacy of <i>Trichoderma azevedoi</i>, <i>T. afroharzianum</i>, <i>T. asperellum</i> and <i>T. asperelloides</i> in inhibiting <i>S. sclerotiorum</i> mycelial growth and sclerotia production. Field experiments then assessed a combination of these antagonists, their alternating application with synthetic fungicides, and a fungicide-alone treatment for disease control, sclerotia reduction and yield increase. In vitro, all four <i>Trichoderma</i> species significantly inhibited the pathogen, achieving 60.1-63.1% mycelial suppression in dual culture and 90.3-94.1% via volatile metabolites, with the latter also completely suppressing sclerotia formation. In the field, the <i>Trichoderma</i> combination significantly controlled white mold, reducing plant incidence and severity to 66.0 and 27.1% in 2021 and 55.6 and 18.8% in 2022, while lowering sclerotia production to 32.7 and 14.6 on ten plants, respectively. This control extended to tubers, where incidence and severity were reduced to 1.6% and 0.4% in 2021, and 1.3% and 0.3% in 2022. The alternating application of <i>Trichoderma</i> with synthetic fungicides proved statistically equivalent to the <i>Trichoderma</i>-alone treatment in disease control, while the fungicides-alone treatment was significantly less effective. Potato yield was highest in plots treated with the <i>Trichoderma</i> combination (46.0 and 52.9 t ha^-1 in 2021 and 2022, respectively). These results highlight the potential of using a mixture of these four <i>Trichoderma</i> species as a cornerstone of sustainable disease management in Sinaloa, offering effective control of potato white mold while significantly reducing dependence on synthetic fungicides.