Parthenium weed (Parthenium hysterophorus L.) is known as an environmental, medical and agricultural hazard around the globe. During 2012-14, a series of surveys were conducted in Haryana, India and a leaf spot disease was regularly reported on parthenium grass in different parts of Kurukshetra, India and its adjoining areas. Pathogen was isolated from the infected leaves on potato dextrose agar) medium. Parthenium leaves were inoculated and the pathogen showed similar symptoms as occurred in nature, proving pathogenicity and Koch’s postulates. Species identification of the pathogen was confirmed by CABI International Mycology Institute and the pathogen was identified as Fusarium solani (Mart.) Sacc. Phytotoxicity of fungal cultural filtrates was also confirmed on parthenium leaves in laboratory conditions. Due to the virulent nature of the isolated pathogen, it may be selected for further studies to develop mycoherbicide for control of this devastating weed.