Introduction: The control of plant pests and diseases is considered one of the fundamental challenges in agriculture, and the widespread use of chemical pesticides to combat these agents entails negative environmental and health consequences. In recent years, biotechnology and the use of natural plant compounds as suitable alternatives to chemical pesticides have attracted increasing attention. Numerous studies have demonstrated that plant extracts and essential oils can play an effective role in controlling plant pathogenic agents. Materials and Methods: The objective of this study was to comparatively evaluate the effects of aqueous extracts of chicory, chamomile, ajwain, Shirazi thyme, Peganum harmala, black pepper, red pepper, Damask rose, and garlic, in comparison with two control treatments (distilled water and a chemical pesticide), on the control of the growth of the fungus Alternaria under in vitro conditions. Aqueous plant extracts were prepared at a concentration of 1 g in 500 mL of water, and 1000 µL of each extract was added to the WA culture medium in 6-cm Petri dishes. Subsequently, fungal colony growth was assessed. Results: The results of analysis of variance and mean comparisons using SAS software indicated that the aqueous extracts of Peganum harmala, ajwain, and black pepper showed no significant difference from the chemical pesticide treatment in controlling the growth of Alternaria at an error level of less than 1% and exhibited performance comparable to that of the chemical pesticide. Conclusion: Based on the results of this study, the aqueous extract of Peganum harmala was identified as the most effective plant-based treatment and was recognized as a suitable and acceptable option for replacing chemical pesticides in the control of Alternaria fungus, and it can be utilized in biological management programs for plant diseases.

Alternaria; Biological Control Pest; Plant Extracts; Medicinal Plants