Antifungal activity of Chromolaena odorata aqueous extract against Alternaria blight (Alternaria brassicae) was examined in vitro and in planta. In vitro, the extract was able to inhibit conidial germination and mycelial growth whereas, in planta, foliar treatment with C. odorata extract reduced disease incidence and severity in Brassica oleracea. Besides the extract, Candida sp. was also tested for its antifungal activity against A. brassicae and it was also efficient against conidial germination and mycelial growth, whereas in planta, no effect was observed on disease incidence and severity. C. odorata extract and Candida sp. had no effect on B. napus seed germination and induction of beta-1,3-glucanase activity.