This study presents the findings of on-farm trials conducted in Hungary between 2023 and 2025, evaluating the efficacy of inundative Trichogramma releases against the European corn borer (ECB) and the cotton bollworm (CBW). The research assessed three Trichogramma preparations, including solo T. brassicae (TB) and two species mixtures: (1) T. dendrolimi, T. cacoeciae, and T. brassicae (TSM1) and (2) T. brassicae and T. pintoi (TSM2). The timing of the releases was synchronized with pest swarming and maize phenology. The efficacy of Trichogramma-based biological control was assessed by comparing the number of damaged plants and the number of pest larvae detected in treated and untreated plots. Statistical analyses revealed a significant association between the release of parasitoids and a reduction in pest damage. The efficacy of the Trichogramma releases was determined using Abbott’s formula. In our research, the following pattern emerged: (1) medium efficacy (ranging from 40% to 68.2%) occurred under low pest pressure and optimal weather conditions; (2) low efficacy (35.5% and 33.3%) occurred under medium pest pressure and suboptimal climatic conditions; and (3) no efficacy occurred under high pest abundance combined with unfavorable weather. Our findings suggest that Trichogramma-based products can serve as complementary components of Integrated Pest Management (IPM); however, they also emphasize that parasitism by Trichogramma wasps is influenced by several factors, such as climatic conditions and pest abundance, indicating that additional plant protection treatments may be necessary, for example, under high pest pressure and/or suboptimal climatic conditions.