When walnut trees are pruned, the resulting wounds are exposed to dangerous fungi that can cause branch die-back and significantly reduce crop yield. This research found that freshly cut pruning wounds are most vulnerable to infection, especially from aggressive fungi like Diplodia mutila, but this vulnerability decreases over time. The fungi spread their spores mainly during wet winter months when rainfall and humidity are high, so timing pruning operations to avoid these periods and protecting wounds with fungicides could substantially reduce disease losses in walnut orchards.