Control of invasive mammals is central to the conservation and restoration of native habitats, especially in unique and vulnerable island ecosystems. While methods for eradication of pest mammals on offshore islands are well-established, long-term suppression at mainland sites and in other locations with an extremely high risk of re-invasion remains challenging. We examined the use of CO2-powered, self-resetting traps for control of rats during a beech forest mast on the New Zealand mainland. Goodnature® A24 automatic traps installed on a 100 × 50-m grid reduced tracking indices for ship rats from 68% to 0% within a 200-ha area over a period of four months. The extent of the trapped area was then increased to 700 ha, with the resolution of the trapping grid reduced to 100 × 100 m. Tracking indices within the expanded area decreased from 44% to 0% within an additional two months. Activity of rats in a non-treatment site remained at around 70% for the duration of the project. Tracking indices for house mice decreased from 22% to 0% within four months and remained low for the duration of the project, indicating that non-targeted control of house mice was also achieved within the project area. Our results show that Goodnature® A24 self-resetting traps can successfully knock down and suppress rats from plague levels within an unprotected, mainland site.