The effect of molasses alone or combined with Trichoderma asperellum T34 Biocontrol® was assessed on Meloidogyne reproduction, disease severity, and density and activity of soil microorganisms in pot and field experiments. Firstly, molasses application at 1 mL m−2 was assessed in four different textured soils. Secondly, molasses application at 5, 10, 20, and 40 mL m−2, alone or combined with T34, was assessed in pot and field experiments at 10 mL m−2 in two different textured soils. The application of 1 mL m−2 of molasses was effective in reducing nematode reproduction in the loam textured soil but not in sandy clay loam, sandy loam, or clay loam textured soils. Increasing molasses dosage reduced the tomato dry shoot and fresh root weights, producing phytotoxicity at 40 mL m−2. The disease severity and nematode reproduction were reduced between 23% and 65% and 49% and 99%, respectively. In the field experiment, molasses applied at 10 mL m−2 reduced the disease severity and the nematode reproduction in the loam textured soil. The soil microbial density and activity did not increase in sites where the nematode reproduction and the disease severity were reduced by molasses application, irrespective of T34.