Open AccessBarnyard grass (Echinochloa crusgalli (L.) P. Beauv.) is a herbicide-resistant weed that brings negative impacts to rice crops and threatens floodplains biodiversity worldwide. This study aimed to investigate allelopathic influences of extracts from Pittosporum undulatum Vent. (cheesewood) leaves on barnyard grass. Leachates in concentrations of 20%, 15%, 10%, 5% and 2.5% (w/v), aqueous extracts from powdered leached and non-leached leaves (10%, 7,5%, 5%, 2.5% and 1.25% for both), coumarin solution at 0.6 mM and original Roundup ® in concentration according to the label information were prepared. Petri-dishes germination bioassays, with counting at each 12 hours, allowed to determinate both germinability and germination rate; polyethylene glycol (PEG 6000) solutions were prepared to evaluate osmotic effects. In growth tests, seedlings were exposed for seven days, when root and shoot lengths were measured. Germination was sensitive to extracts from powdered leaves. In regard to growth, roots showed dose-dependent length reduction and necrosis. Inhibitory effects from different aqueous extracts suggest action of both internal and external leaf allelochemicals, raising the possibility of Pittosporum undulatum use for barnyard grass control.