On Friday, August 22, 2025, the annual “Apfeltag” (Apple Day) took place at Campus Klein-Altendorf in Rheinbach, hosted this time by Bio Innovation Park Rheinland e.V., the Dienstleistungszentrum Ländlicher Raum Rheinhessen-Nahe-Hunsrück (DLR R-N-H), the University of Bonn, and the Agricultural Chamber NRW. More than 200 visitors, consultants, and organizers were offered a diverse program of specialist presentations during tours through the orchards, as well as exhibits from over 50 participants.
After a welcome by Andy Becht, State Secretary of the MWVLW RLP, Prof. Klaus Sandmann, Vice-Rector of the University of Bonn, Dr. Arne Dahlhoff, Director of the Agricultural Chamber NRW, as well as local political representatives, District Administrator Sebastian Schuster and Mayor Holger Jung from Meckenheim, guided tours in the morning provided updates on topics such as the Mediterranean fruit fly and pear leaf sucker, harvesting technology, mechanical fruit thinning, robotics, and innovations from various exhibitors.
HortiBonn was involved in the station on mechanical fruit thinning. At this station, Philipp Wolf (DLR R-N-H) and Thomas Beyel (University of Bonn) presented experiments with two vibrating machines for late mechanical thinning of apples. The trials showed that the efficiency of mechanical fruit thinning after the June drop depends on the variety, fruit size, tree habit, and device settings. The thinning effect is greater with larger fruits, so in practice, treatments can be effective at fruit sizes of approximately 40–50 mm. Mechanical fruit thinning can save up to 20% of the time required for subsequent manual or quality thinning.
In addition to the practical results, Dr. Thorsten Kraska (HortiBonn) presented findings on the influence of fruit thinning machines on the electron transport rate as an indicator of photosynthetic performance and on the transpiration of the remaining apple leaves, which are now more exposed to light. Both the electron transport rate and transpiration were increased by fruit thinning at most measurement points. Visitors were also able to view the machines and get an impression of this still relatively new technology. An autonomous grass mulcher and crop protection sprayer also attracted considerable attention.
In the afternoon, a special thematic block addressed the topic of climate adaptation in fruit growing and strategies for water storage. The HortiBonn team’s contribution, which focused on the ecological enhancement of irrigation ponds, was presented by Christine Schmitz (HortiBonn, DLR Rheinpfalz) and Dr. Jürgen Lorenz (DLR R-N-H). The results of a decision analysis highlighted the importance of irrigation for profitable apple cultivation. They showed that the ecological enhancement of a foil pond incurs only minimal additional costs while significantly increasing biodiversity. Where soil conditions allow for the construction of a near-natural storage basin, these are most advantageous from both an economic and ecological perspective.
In addition to scientific contributions from the HortiBonn team, Factflow, a start-up that emerged from the working group, participated as an exhibitor. The Factflow team (Johannes Kopton, Dr. Katja Schiffers, and Alexa Leyens) demonstrated how they can prepare a life cycle assessment based on a farm’s CAP applications.
