Impact of Planting Time on Severity of Alternaria Blight and Yield Losses in African Marigold (Tagetes erecta)

Alternaria blight, caused by Alternaria tagetica, poses a significant threat to marigold production, leading to substantial losses in flower yield. The present study aimed to evaluate the impact of different transplanting months on Alternaria leaf blight severity, flower blight incidence and yield losses in marigold. Results indicated that transplanting the crop in October month resulted in the highest leaf blight severity (89.00% ± 1.87%), flower blight incidence (59.30% ± 1.84%) and disease progression (AUDPC = 4259.50 ± 53.37), while February and March transplanted crops had the lowest disease severity (9.13% ± 1.11% and 15.13% ± 1.89%, respectively). Marketable flower yield varied significantly with transplanting months and highest marketable flower yield was observed in August (207.21 ± 1.17 q/ha), whereas the lowest was in December transplanting (17.60 ± 1.17 q/ha). The application of carbendazim effectively reduced disease severity and increased the marketable floral yield in protected plots compared to unprotected ones. Avoidable floral yield losses due to Alternaria infection ranged from 11.23% to 58.90% across different transplanting months, being highest in October. Correlation analysis revealed that disease severity was positively correlated with morning relative humidity (r = 0.93) and evening relative humidity (r = 0.59) while it was negatively correlated with maximum temperature (r = −0.76), wind speed (r = −0.94) and sunshine hours (r = −0.84). Principal component analysis indicated that high morning humidity and wind speed are the main drivers of Alternaria blight severity. These findings demonstrated that months with the highest yield potential are also congenial for the pathogen to cause infection. Marigold growing farmers can minimise financial losses by regularly monitoring their crops and transplanting crops to less favourable climatic conditions for disease development.