Assessment of Chemical and Biological Fungicides for the Control of Diplodia mutila Causing Wood Necrosis in Hazelnut

Fungal trunk disease (FTD) poses a significant threat to hazelnut (Corylus avellana L.) production worldwide. In Chile, the fungus Diplodia mutila, from the Botryosphaeriaceae family, has been frequently identified causing this disease in the Maule and Ñuble Regions. However, control measures for D. mutila remain limited. This research aimed to evaluate the effectiveness of chemical and biological fungicides against D. mutila under in vitro, controlled pot experiment, and field conditions. An in vitro screening of 30 fungicides was conducted. The effectiveness was assessed by measuring the length of vascular lesions in hazelnut branches inoculated with D. mutila mycelium disks under controlled and field conditions. Field trials were conducted in a hazelnut orchard in Ñiquén, Ñuble Region, Chile. Results showed that three biological and five chemical fungicides were selected in vitro with > 31% inhibition after 14 days. In pot experiments, all fungicides reduced necrotic lesions on branches by 32 to 61%. In field experiments, the most effective systemic fungicides were fluopyram/tebuconazole, fluxapyroxad/pyraclostrobin, and tebuconazole, while the effectiveness of antagonists Pseudomonas protegens ChC7 and Bacillus subtilis QST713 varied with seasonal temperatures. Effective conventional and biological fungicides against D. mutila could be integrated into disease management programs to protect hazelnut wounds from infections.