Field Evaluation of Fungicides for the Management of Purple Blotch Disease of Onion Seed Crop Caused by Alternaria porri

Purple blotch, caused by Alternaria porri (Ellis) Cif., is a major disease affecting onion seed production. A field experiment was conducted at the Research Farm of the Department of Plant Pathology, Junagadh Agricultural University, Junagadh, to evaluate the efficacy of eight fungicidal treatments against purple blotch in the ‘Pilipati’ onion cultivar, with an untreated control included for comparison. The experiment was laid out in a randomised block design with three replications. Onion bulbs were planted on 2 December 2025, and artificial inoculation was carried out on 5 January 2026. Fungicides were applied at disease onset, followed by two additional applications at 15-day intervals. Disease intensity was assessed seven days after the final spray, and seed yield was recorded at harvest. All fungicidal treatments were associated with lower disease intensity and higher seed yield than the untreated control. Tebuconazole 50 + trifloxystrobin 25 WG at 0.1 per cent recorded the lowest disease intensity (12.48%) and highest seed yield (670 kg ha⁻¹). Azoxystrobin 18.2 + tebuconazole 18.30 SC at 0.025 per cent recorded 17.28% disease intensity and a seed yield of 657 kg ha⁻¹ and was statistically comparable to the former treatment. The untreated control recorded 68.49% disease intensity and 428 kg ha⁻¹ seed yield. These findings indicate that the two leading fungicide combinations provided comparatively favourable disease and seed-yield outcomes under the conditions of this field trial.