Efficacy of selected fungicides and antibacterial chemicals against Fusarium verticillioides, Macrophomina phaseolina and Dickeya zeae associated with maize stalk rot

Abstract

Maize stalk rot is a devastating disease complex caused by the co-infection of fungal and bacterial pathogens, severely threatening global maize production. This study evaluated the in vitro efficacy of eleven fungicides (at 100%, 50%, and 25% of the recommended field rates) against Fusarium verticillioides and Macrophomina phaseolina using the poisoned food technique. Concurrently, five antibacterial agents were screened against Dickeya zeae using a disc diffusion assay under a Completely Randomized Design (CRD). In vitro screening revealed that tebuconazole 38.39 SC, thiophanate-methyl 70 WP, azoxystrobin 18.3 + difenoconazole 11.4 SC, trifloxystrobin 25 + tebuconazole 50 WG, and captan 70 + hexaconazole 5 WP formulations exhibited superior antifungal activity, achieving over 90% mycelial growth inhibition against the key post-flowering stalk rot pathogens Fusarium verticillioides and Macrophomina phaseolina even at 50% of their recommended field dosages. Probit analysis corroborated this, with EC50 values of the top-performing fungicides against both pathogens consistently falling below 25% of the recommended field dose, indicating scope for effective disease control at reduced dosages. Against the bacterial pathogen D. zeae, copper oxychloride 50 WP at 0.3% emerged as the most effective non-antibiotic treatment, achieving 71.0% relative efficacy relative to positive control, Plantomycin @ 250 ppm (Streptomycin Sulphate 9% + Tetracycline Hydrochloride 1% SP), followed by bleaching powder at 3% (66.1%) and copper hydroxide 46.1 WG at 0.2% (41.9%). These baseline in vitro findings identify highly potent, broad-spectrum chemical candidates for managing the maize stalk rot complex. Further validation under greenhouse and natural field conditions is warranted to incorporate these molecules into sustainable integrated disease management (IDM) strategies.