Pest forecasting is of paramount importance in tobacco production in Vietnam, as it contributes to reducing yield and quality losses. During the 2025 cropping season, the Vietnam Tobacco Institute applied Growing Degree Days (GDDs), weather climatic and leaf wetness (LW) model to predict outbreaks of the tobacco budworm (Helicoverpa assulta) and powdery mildew (Erysiphe cichoracearum) in the provinces of Cao Bang, Gia Lai, and Tay Ninh. The integrated forecasting models achieved an accuracy exceeding 91%. Specifically, budworm development was best predicted using the GDD model combined with weather climatic model, whereas powdery mildew disease was forecasted using models incorporating weather climatic and leaf wetness. Climatic variables played a decisive role in determining the occurrence and severity of tobacco budworm. Temperature, relative humidity, rainfall, and rainy days were identified as the most influential factors. In contrast, for powdery mildew, in addition to these variables, leaf wetness duration (LW) and the temperature during LW periods were critical parameters to enhance the forecasting accuracy. The GDD model performed most effectively when daily temperatures fluctuated within the pest’s biological development thresholds (TL UT), with the highest accuracy observed within the optimal thermal range. Forecasting accuracy reduced when temperatures exceeded the optimal temperature range and became unreliable when temperatures rose over the upper biological threshold of the insect. Based on these findings, the Vietnam Tobacco Institute recommended integrated pest management strategies for tobacco production companies. These strategies aim to minimize crop losses while reducing reliance on chemical pesticides in major tobacco-growing areas. As a result, in the 2025 season, infestations of tobacco budworm and powdery mildew were limited to low or negligible levels, with only minimal effects on yield and quality in Vietnam.