Fungicide screening against tobacco brown spot

To screen highly effective fungicides against tobacco brown spot caused by Alternaria alternata, indoor toxicity and field efficacy of five common fungicides (fluazinam, picoxystrobin, boscalid, cyprodinil and famoxadone) against A. alternata were determined. The results showed that fluazinam had the strongest inhibitory activity against mycelial growth, around 98%; this was followed by cyprodinil and famoxadone at 95%. The EC₅₀ of 98% fluazinam, 95% cyprodinil and 95% famoxadone for the mycelial growth of A. alternata were 0.138 2, 3.568 9 and 30.098 3 mg/L, respectively. The control efficacy of 50% fluazinam SC and 62% cyprodinil WG in field trials reached 70.44% and 63.09%, respectively. The field control efficacy of 50% boscalid WG was the worst, at only 39.53%. On the basis of these results, fluazinam and cyprodinil were recommended to control tobacco brown spot.