Evaluation of chemical and biological control strategies against leaf spot in niger incited by Alternaria alternata

Niger (Guizotia abyssinica L.) is a traditional minor oilseed crop predominantly cultivated in
tribal regions of India. Under conducive environmental conditions, niger is susceptible to
various diseases, among which leaf spot caused by Alternaria alternata is one of the most
predominant, leading to significant yield losses. In recent years, the area under niger
cultivation has increased in the Konkan region of Maharashtra; however, there is a limited
availability of crop-specific fungicidal recommendations. Additionally, there is a pressing
need for effective, eco-friendly disease management alternatives suitable for smallholder
farming systems. Therefore, the present investigation was undertaken to evaluate the efficacy
of fungicides and bio-agents against leaf spot disease, both under in vitro and field
conditions. In the in vitro studies, complete inhibition of Alternaria alternata was observed
with treatments of Hexaconazole 5% EC at 0.1%, Carbendazim 12% + Mancozeb 63% WP at
0.2%, and Hexaconazole 4% + Zineb 68% WP at 0.1%. Among the seven bio-agents tested,
Pseudomonas fluorescens strain-4 proved to be the most effective, recording the least
mycelial growth (22.16 mm) and the highest inhibition (75.36%) of A. alternata. The most
promising treatments from the in vitro evaluation were subsequently selected for field trials,
integrated with seed treatment. All tested treatments were significantly superior to the
untreated control. The lowest disease severity (6.87%) and the highest disease reduction
(84.94%) were achieved with seed treatment using Captan 50% WP at 4 g/kg, combined with
two foliar sprays of Tebuconazole 50% WG + Trifloxystrobin 25% WG at 0.05%. A
comparable level of control was obtained with seed treatment using Captan 50% WP at 4
g/kg, followed by two sprays of Carbendazim 12% + Mancozeb 63% WP at 0.15%, which
resulted in 8.70% disease severity and 80.93% disease reduction compared to the control.