Pre-harvest dynamics of Aspergillus section Flavi and aflatoxin risk in hazelnut orchards of Azerbaijan

Hazelnuts (Corylus avellana L.) are susceptible to aflatoxin contamination, with recurrent notifications reported in Azerbaijan. A three-year study (2023–2025) was conducted in 30 orchards across three main hazelnut-producing districts to investigate the pre-harvest dynamics of Aspergillus section Flavi. Fungal populations were monitored at four phenological stages (BBCH 70–89), and aflatoxin levels were assessed at harvest and late-harvest. Fungal abundance and incidence were significantly affected by geographical area, year, and growth stage (P < 0.01). A. section Flavi populations were higher in warmer districts such as Qabala and Zaqatala (up to 1.7 Log10 CFU/g) compared with Khachmaz (1.0 Log10 CFU/g), with relative incidence reaching 13.8% in Zaqatala. Fungal abundance peaked during nut filling (BBCH 79), reaching 2.4 Log10 CFU/g, with a corresponding incidence of 18.5%. Marked interannual variability was observed, with A. section Flavi incidence increasing from 1.2% in 2023 to 40.8% in 2024. Despite the frequent isolation of A. section Flavi, aflatoxin levels in standard orchard samples collected at BBCH 89 remained generally below EU limits (≤5 μg/kg). In contrast, late-harvest samples showed markedly higher contamination, with total aflatoxin concentrations ranging from 71.2 to 752.8 μg/kg, particularly in ground-collected nuts. These findings indicate that pre-harvest aflatoxin risk is primarily driven by orchard microclimate and harvest timing, highlighting the importance of Good Agricultural Practices, timely harvest, and rapid post-harvest drying.