-Parthenium (Parthenium hysterophorus) is an alien invasive weed infesting many parts of the world including Pakistan. A number of herbicides have been recommended for control of this weed, but these herbicides have issues regarding human health and environmental safety. In the current study, the herbicidal potential of culture filtrates of a fungal species, namely Alternaria japonica, was evaluated against parthenium weed. The fungal species was grown in malt extract broth (MEB) and potato dextrose broth (PDB) for 15 days. Culture filtrates were obtained by passing the materials through muslin cloth followed by filtration through filter paper and then through Millipore filter paper. In laboratory bioassays, the effect of original (X) and diluted (½X) filtrates was studied on seed germination, and shoot and root growth of parthenium. In general, fungal culture filtrates prepared in either of the two growth medium significantly reduced germination and seedling growth of parthenium. However, culture filtrates prepared in potato dextrose broth showed greater herbicidal activity than those prepared in malt extract broth. Foliar spray bioassays were carried out by using culture filtrates of A. japonica prepared in potato dextrose broth. In this experiment, 1-, 2-and 3 week old parthenium seedlings were sprayed 4 times with original (X) and concentrated (2X) fungal culture filtrates, with intervals of 4 days. In general, 1 week old parthenium seedlings were highly susceptible to foliar spray of fungal metabolites. The present study concludes that culture filtrates of A. japonica prepared in potato dextrose broth contain potent herbicidal constituents for management of parthenium.Keywords: Asteraceae, congo grass, fungi, mycoherbicide, weed. Palavras-chave: Asteraceae, capim-do-congo, fungos, mico-herbicida, planta daninha. RESUMO -A losna-branca (Parthenium hysterophorus) é uma espécie invasora não nativa que infesta várias partes do mundo, incluindo o

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