Field trials were set up in the humid forest zone of Cameroon to investigate the effects of combinations of different rates of nitrogen (N) (0, 60, and 120 kg N ha⁻¹) and potassium (K) (0, 80, and 160 kg K ha⁻¹) applied to the soil on the incidence and damage of the noctuid stemborer Busseola fusca (Fuller), and on maize, Zea mays L., yield. Each N/K combination had an insecticide control to assess yield losses due to borers. In contrast to N, K had no effect on plant growth and borer incidence and damage. Across seasons and days after planting, total plant dry matter (DM) production increased with N level and it was 1.2–1.9 and 1.7–2.2 times, respectively, higher at 60 and 120 kg N ha⁻¹ compared with 0 kg N ha⁻¹. Total DM at harvest was strongly related to the N content of the plant at 63 d after planting. At the early growth stage, borer abundance and stem tunneling tended to increase with N level, but percentages of dead hearts did not vary with treatment. Maize grain yields increased linearly with N level, but grain yield losses decreased depending on season. Grain yield losses were 11–18.2 times higher with 0 kg N ha⁻¹ compared with 120 kg N ha⁻¹. The findings so far indicated that, soil application of N improves the nutritional status of maize, which consequently enhanced its tolerance to stemborer attacks. Improving soil fertility can thus be a very effective means of complementing integrated stemborer control in the humid forest zone of Cameroon.