<p>Late blight, caused by <i>Phytophthora infestans</i>, poses a significant threat to global tomato (<i>Solanum lycopersicum</i> L.) production, leading to substantial yield losses. This study evaluates the impact of late blight on tomato yield, tracks disease progression, and examines the influence of environmental conditions to enhance disease management strategies. Field experiments were conducted over two growing seasons at the ICAR Research Farm, Arunachal Pradesh, using the highly susceptible cultivar, Pusa Ruby. Disease severity was monitored from standard metrological week (SMW)-1 to SMW-5 under natural epiphytotic conditions, with yield loss assessments and correlations to weather parameters. Our findings reveal that disease progression followed a Gompertz growth model (R² = 0.94), with cumulative rainfall (<i>r</i> = 0.679) and relative humidity (<i>r</i> = 0.703) exhibiting a strong correlation with disease severity. Multiple fungicide applications significantly reduced disease severity and improved yield, whereas a single application had limited efficacy due to premature timing. These results emphasizing the critical role of environmental factors in disease escalation and the necessity of integrated disease management strategies. This study provides a predictive framework for managing late blight outbreaks and safeguarding tomato production.</p>