Toxicity evaluation and control efficacy of seven fungicides against tobacco root rot caused by Aphanomyces iridis at seedling stage

In order to screen efficient fungicides with low toxicity that can prevent and control root rot of tobacco seedlings caused by Aphanomyces iridis, the toxicities of 70% thiophanate-methyl wettable powder(WP), 58% metalaxyl-mancozeb wettable powder(WP), 50% chlorobromo isocyanuric acid soluble powder(SP), 20% cinnamamide hydrochloride solution(AS), 30% propamocarb-azoxystrobin suspension concentrate (SC), 80% enoylmorpholine water dispersible granules (WG), and 48% propamocarb-cupric-ammonium solution(AS)against A.iridis were tested by the mycelial growth rate method. Simultaneously, control efficacy and safety were evaluated by inoculation into floating seedlings. The results showed that 48% propamocarb-cupric-ammonium solution and 30% propamocarb- azoxystrobin had the strongest inhibitory efficacy against the mycelium of A.iridis with EC₅₀ values of 0.255 and 0.367 μg/mL, respectively. This was followed by 20% cinnamamide hydrochloride and 58% metalaxyl-mancozeb with EC₅₀ values of 14.107 and 37.495 μg/mL, respectively. The antifungal effect of 70% thiophanate-methyl was the worst. The result of inoculation experiment showed that 48% propamocarb-cupric-ammonium solution and 30% propamocarb-azoxystrobin had a good control efficacy on root rot of tobacco seedlings caused by A.iridis with control efficacy ranging from 86.88% to 94.61%, and the treatment of 30% propamocarb-azoxystrobin had good safety for tobacco seedlings. The control efficacy of 58% metalaxyl-mancozeb was poor, being less than 30%.