The present invention provides an isolated biocontrol agent, which is a strain of Pyricularia setariae. The present invention also relates to a biocontrol composition comprising at least one fungal biocontrol agent, which is a strain of Pyricularia setariae. Examples of the biocontrol agent of the present invention include Pyricularia setariae 94-409A (IDAC 190701-1), Pyricularia setariae 01-069A (IDAC 290102-01), and Pyricularia setariae 01-071A (IDAC 290102-02). Preferably, the biocontrol composition comprises an acceptable medium such as a liquid culture medium or a solid culture medium. The biocontrol agent or biocontrol composition may be used to suppress the growth of a weeds such as green foxtail (Setaria viridis [L.] Beauv.).