Pruning practices in European hazelnut: from plant shape and planting layout to mechanical pruning and precision agriculture

Hazelnut is a suckering plant that tends to develop into a multi-stemmed bush, and its vegetative habit is often changed by growers when establishing and managing commercial orchards. In some producing areas, growers prefer trees with a single trunk and open V-shape. This shape facilitates mechanical harvesting and permits more sunlight penetration within the rows. Conversely, training as a multi-stemmed bush allows the grower to renew the plants gradually, eliminating the old stems and replacing them by selecting new lignified suckers. The orchard dynamic spacing has been recently explored for hazelnut to reduce its juvenility period after planting. Hazelnut pruning is usually done during winter through the removal of suckers, diseased or dead wood, and badly oriented branches. A lack of regular pruning causes a reduction in shoot vigor and drastically reduces light penetration within the tree canopy, reducing yield and nut quality and increasing the biennial bearing tendency. With these in mind, the most common training systems adopted in the main hazelnut growing areas are explored, including recent attempts to manage hazelnut orchards at high-density and at dynamic tree spacing, as well as applications of mechanical pruning and automatic pruning protocols for large-scale hazelnut orchards developed by the project H2020 PANTHEON.