Rice seedlings (10 g fresh weight) were homogenized in 100 mL 50% (v/v) cold aqueous methanol and the homogenate was filtered through filter paper (No. 2; Toyo Ltd., Tokyo, Japan). The residue was homogenized again with 100 mL of methanol and filtered and the two filtrates were combined. An aliquot of the extract was evaporated to dryness, dissolved in 0.2 mL of methanol and added to a sheet of filter paper (No. 2) in a 3-cm Petri dish. Methanol was evaporated in a draft chamber. Then, the filter paper in the Petri dishes was moistened with 0.8 mL of a 0.05% (v/v) aqueous solution of Tween 20. The final assay concentration was one rice plant equivalent extract per mL. After germination in the darkness at 25 ◦C for 120 h, 10 uniform barnyard grass seedlings were placed into the Petri dishes. The length of their shoots and roots was measured after 48 h of incubation in the darkness at 25 ◦C. Inhibitory activity (%) was determined by the formula: [(control plant length − plant length treated with rice extract)/control plant length] × 100. Control bioassays did not contain rice extracts. The bioassay was repeated six times using a completely randomized design with 10 plants for each determination. Significant differences were evaluated by Tukey’s HSD test.