In-vitro and field evaluation of foliar fungicides for the management of Alternaria leaf blight in Radish (Raphanus sativus L.)

Radish, a member of the Brassicaceae family, is a widely cultivated edible root vegetable. Despite its popularity, radish cultivation faces significant challenges due to various pests and diseases, majorly Alternaria leaf blight (ALB) caused by Alternaria brassicicola. To overcome this challenge, an evaluation of eight fungicides consisting of three contact (Chlorothalonil, Propineb, Copper oxychloride), four systemic (Azoxystrobin, Hexaconazole, Propiconazole, Tebuconazole) and a combination (Metalaxyl-M + Mancozeb), was carried out against ALB under in-vitro and field conditions. The efficacy of eight fungicides at varying concentrations (100, 250, 500 and 750 ppm) in inhibiting mycelial growth and conidial germination of A. brassicicola was evaluated. The results showed Tebuconazole to be the most effective fungicide in inhibiting both mycelial growth (100%) and conidial germination (90.70%) at the highest concentration, followed by Propiconazole, Azoxystrobin and Hexaconazole with EC₉₀ of 89.9, 98.8, 105.6, and 101.2 μg mL⁻¹, respectively. Fungicides such as Tebuconazole, Propiconazole and Azoxystrobin had higher conidial germination inhibition, with lower EC₅₀ of 177.2, 198.2 and 200.7 μg mL⁻¹, respectively. To confirm these findings, field trials were conducted over two growing seasons. The foliar spraying of Tebuconazole at 1 ml/L significantly outperformed other treatments, resulting in the lowest PDI (7.67%) and highest radish root yield (13.62 tons/ha). Propiconazole and Azoxystrobin treatments also showed promising results, while untreated controls exhibited the lowest yields of 8.83 tons/ha. Based on the study and information generated, Tebuconazole at 1 ml/L could be recommended and incorporated as a preventive or curative measure in radish ALB management programs.