Control of gray mold caused by Botrytis cinerea in hazelnut orchards in Düzce province

This study was conducted to determine the prevalence, pathogenicity, and sensitivity of the grey mold pathogen Botrytis cinerea to selected fungicides and biological control agents in hazelnut (Corylus avellana L.) production areas of Düzce province and its districts. During the 2022 production season, survey studies were carried out in 166 orchards across 8 districts, and a total of 72 B. cinerea isolates were obtained from 163 samples. Pathogen identification was confirmed by morphological and molecular analyses. Pathogenicity tests were performed on seven representative isolates selected from the total isolate collection. Among them, isolate 2B2 showed the highest disease severity in nut cluster, leaf, and husk assays. Fungicide sensitivity tests conducted with this isolate revealed that tebuconazole (73.30% inhibition at 1 µg/mL) and thiophanate-methyl exhibited the strongest inhibitory effects. In biological control assays, Trichoderma harzianum KRL AG-2 completely suppressed disease development, while Pythium oligandrum M1 was also found to be highly effective. The results demonstrate that B. cinerea poses a significant phytopathological threat to hazelnut production areas in Düzce and that certain biological control agents may serve as potential alternatives to chemical fungicides. This study provides scientific support for the development of integrated disease management strategies toward sustainable hazelnut production.