Abstract: The incidence of leaf spot of mustard (cv. BARI sharisha 13) grown in different orientations and distances under around twelve years old Akashmoni (Acacia auriculiformis) tree was studied in the field laboratory of the Department of Agroforestry, BAU, Mymensingh during 2004-05. The assessment result showed that the disease incidence was higher near the tree base in every side (1 m from the tree base) and higher in North side in all distances at different date of sowing. The lowest disease incidences were found in South orientations 3 m from the tree base and highest in North 1 m from the tree base. The siliqua infection significantly influenced on crop yield. The highest seed yield was observed in South orientation 3 m from the tree base and lowest in North 1 m from the tree base plot. The distance and orientation showed marked effect in disease development at different date after sowing. In open field condition (control) disease incidence also affect on yield and statistically different from tree-crop combination.