Technical Abstract: Phomopsis longicolla is a major seed pathogen of soybean in hot and humid production environments. This study was conducted for three years to monitor the infection and development of P. longicolla on vegetative and reproductive tissues of six cultivars and determine the relationship between this infection and subsequent seed infection and seed germination. Cultivars were grown in plots that were non-irrigated, irrigated between growth stages VC and R6, and R1 and R6. Phomopsis longicolla was isolated from leaves, stems, and roots 3 weeks after planting and was recovered from pods at the R1 stage. Phomopsis longicolla recovery from roots was much lower compared to other plant parts in all years and irrigation regimes. Isolations made from pods was highly correlated with seed infection across years (r= 0.62, r= 0.63 and r= 0.55, P=0.05, for 2002, 2003 and 2004, respectively). There were differences among irrigation regimes for the recovery of P. longicolla from leaves, stems and roots and pods. However, the recovery of P. longicolla from seeds was strongly associated with irrigation regimes. Seeds from irrigated plots had more P. longicolla than those from non-irrigated plots. Phomopsis longicolla from seed was negatively correlated with percent seed germination in 2002 (r=-0.80, P=0.05) and 2003 (r=-0.93, P=0.05). This study indicates that seed infection by P. longicolla was more moisture dependent than infection of the vegetative plant parts.