Ethephon Application on Hazelnut (Corylus avellana L.) Trees: Productive and Physiological Experience in a Temperate Climate Zone

Chile contributes 4% of global hazelnut (Corylus avellana L.) production, mainly developed in temperate regions with high autumn rainfall and humidity during harvest, which can compromise nut quality and increase postharvest losses. Thus, synchronizing harvests has become a critical aspect for growers in the southern region of Chile. This study focused on the effects of ethephon (ETH) spraying on trees to optimize nut drop timing and assess its impact on yield optimization and its influence on vegetative growth and inflorescence activity. From the 2020/2021 to the 2022/2023 seasons, experiments were conducted on a commercial hazelnut orchard of Tonda di Giffoni (TDG) planted in southern Chile. Four ETH (0, 250, 500, 1000 mg L−1) treatments were sprayed 15 days preharvest and denoted as ETHA (sprayed 2020/2021) and ETHB (sprayed twice, in 2020/2021 and 2021/2022). Nut drop synchronization was periodically monitored at 7, 15, 21, 28, and 35 days after application (DAA), along with industrial quality parameters (nut weight, kernel yield) and inflorescence activity. In the first season, ETH significantly synchronized nut drops, achieving optimal results at 15–28 DAA with ETH 250 and 500, while ETH 1000 induced earlier drops but reduced yields. Total nut yield varied among seasons and demonstrated consistent performance of ETH 250, identified as the most efficient treatment for balancing nut drop timing. Industrial parameters showed seasonal differences but no adverse effects on nut quality. Conversely, the inflorescence activity remained unaffected by ETH concentrations. ETHA and ETHB treatments influenced tree shoot length variably across three seasons, showing significant concentration and seasonal interaction effects. These results demonstrate that ETH effectively synchronizes hazelnut harvests under temperate conditions, reducing post-harvest losses and optimizing logistics without compromising yield or quality.