In vitro effectiveness of difenoconazole against Itersonilia perplexans Derx

Abstract

Leaf blight caused by Itersonilia perplexans Derx is commonly observed on dill (Anethum graveolens L.) at the crop maturity stage. In the fields of southern Italy, I. perplexans attacks begin in late autumn, when the weather is cool and humid. In laboratory, the fungal growth rate was maximum at 20 °C, the ballistoconidia production was null at temperatures of 25 °C or higher, and growth was interrupted at 30 °C or above. It is difficult to manage the disease because very few fungicides are admitted for use on dill. Therefore, we screened in vitro several fungicides for their toxicity against I. perplexans, and discovered the high effectiveness of difenoconazole, with EC₅₀ and EC₉₅ of 0.5 and 0.95 μg mL⁻¹, respectively, both for mycelium growth and ballistoconidia production. Ciprodinil+fludioxonil, azoxystrobin (both with EC₅₀ = 0.69 μg mL⁻¹) and boscalid (EC₅₀ = 7.32 μg mL⁻¹) were toxic to I. perplexans, but did not suppress completely the pathogen even at doses of 10,000 μg mL⁻¹. Mancozeb+metalaxil showed EC₅₀ of 15.5 μg mL⁻¹ and completely suppressed the fungus at 100 μg mL⁻¹. Copper oxychloride was toxic only at doses higher than 100 μg mL⁻¹, and sulphur did not affect the pathogen growth. Therefore, difenoconazole is worthy of further evaluations in the field for the control of leaf blight of dill caused by I. perplexans.