Widespread Occurrence of European Corn Borer ( Ostrinia nubilalis ) and Damage of Industrial Hemp ( Cannabis sativa ) Crop in Northern Europe

Industrial hemp cultivation restarted in Estonia in mid 2000s and the hemp cultivation area has increased very fast in recent years, but it is unknown to what extent hemp productivity can be curbed by widespread crop pests. Thus, the main aim of this study was to evaluate the presence and damage of hemp pests in northern field conditions. A field trial with the hemp cultivars ‘Finola’ (2021) and ‘Estica’ (2022) was established in Central Estonia (58° N, 26° E), and the plants were grown with different fertilizer types (complex fertilizer, ammonium nitrate), fertilization methods (at sowing/top dressing) and nitrogen rates (0–200 kg ha −1 ) and their effect on the European corn borer (ECB, Ostrinia nubilalis ) damage was assessed. The O. nubilalis infestation increased with every observation date throughout the seasons until the harvest. The O. nubilalis damage was overall greater in 2022 than in 2021, and the seed yield reduction reached to 120 kg ha −1 in 2022, indicating progressive increase in O. nubilalis damage. Fertilization rate strongly increased biomass and seed yields, but weakly reduced O. nubilalis infection. Estonia is one of the most important hemp-cultivation areas in Europe, and in northern conditions, the crop was previously considered to be relatively pest-free. The northward movement of crop infection by O. nubilalis implies that future hemp cultivation might need integrated O. nubilalis control practices adapted to site-specific agro-climatic conditions.