Background: Parthenium hysterophorus is a fast-spreading invasive weed that poses serious challenges to agriculture and the environment due to its aggressive growth and allelopathic effects. The conventional use of mechanical or chemical methods for its control, often result in environmental hazards and some times limited effectiveness of these methods. As a sustainable alternative, biological management using pathogenic fungi is gaining attention due to its specificity and ecological safety. 
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Methods: The study aimed to isolate and evaluate pathogenic fungi from infected Parthenium plants to assess their potential as biological control agents. Four fungal isolates were collected from naturally infected Parthenium plants and tested for pathogenicity on Parthenium, using the disc plate technique under controlled laboratory conditions. 
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Result: Results revealed that Alternaria macrospora strain PHMMU1 exhibited the highest disease incidence (67.27%) and most severe defoliation, followed by Alternaria alternata strain PHMMU2 (50.06%), A. macrospora strain PHMMU3 (40.70%) and A. macrospora strain PHMMU4 (35.18%). All isolates fulfilled Koch&rsquo;s postulates, confirming their pathogenicity. The findings highlight the potential of Alternaria spp., particularly A. macrospora, as effective mycoherbicides for the sustainable management of Parthenium hysterophorus, supporting integrated weed management strategies and environmental conservation efforts. 
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Exploiting Phytopathogenic Alternaria alternata and Alternaria macrospora for Management of Parthenium hysterophorus