Floriculture has emerged as a lucrative source of income for farmers and is experiencing significant growth in the Jammu Valley of the North Western Himalayan region. Marigold (Tagetes erecta L.) stands out as a major ornamental crop cultivated in agro-climatically diverse areas, subjecting the plants to various abiotic and biotic stresses. Among these stressors, leaf spot and flower blight caused by Alternaria tagetica pose a substantial economic threat. Therefore, conducting periodic surveys to assess disease incidence and severity becomes imperative. Fortnightly surveys were carried out in key marigold-growing areas of Jammu, including Jammu, RS Pura, Bishnah, and Akhnoor block in Jammu district. The findings revealed an average disease incidence of 49.90% and 49.40% during the years 2017-18 and 2018-19, respectively. The impact of plant age on disease progression indicated that maximum leaf spot severity reached 57.50% and 58% in 2017-18 and 2018-19, respectively. Similarly, the maximum flower blight incidence recorded was 43.75% and 43.60% during the same periods, highlighting a correlation between disease development and plant age. The study underscored the significant role of environmental parameters—temperature, relative humidity, and rainfall—in disease development. During 2017-18, these parameters accounted for 51.0% and 94.2% influence on leaf spot and flower blight disease, respectively. In 2018-19, the respective percentages were 71.1% and 92.9%, confirming the impact of environmental factors on disease dynamics. The field experiment further validated these findings on the susceptible cultivar Pusa Basanti. Understanding these dynamics is crucial for developing effective strategies to mitigate the economic losses caused by leaf spot and flower blight in marigold cultivation in the North Western Himalayas.