New methods of environmentally safe regulation of flower and fruit set and of alternate rearing of the apple crop

It is well documented that flower and fruit set have a major impact on fruit quality and regularity of bearing of apple trees (Malus domestica Borkh.) and that flower and fruit thinning help to avoid alternate bearing and improve fruit quality. Efficient, chemical-free newer and fruit thinning methods would help to further reduce chemical inputs in integrated fruit production and to reduce production costs and alternate bearing in biological (organic) apple orchards. This paper is a progress report on several approaches which we study including selected results: i) Various ways of hand flower thinning, ii) mechanical flower thinning with a thinning machine, iii) shading trees from light admittance to enhance fruit abscission, and iv) pruning at different dates to regulate flower induction and bud differentiation. Hand thinning strategies were effective in regulating alternate bearing with cvs. Boskoop and Elstar which tend to crop every second year and an difficult to regulate, but this approach is labour intensive and cultivar particularities need to be respected. Some practical recommendations can be made regarding the use of a thinning machine. Shading of orchard apple trees at particular dates affected June drop significantely, but further basic studies are required to value the potential of this approach for practical apple growing. Pruning procedures allowed to manipulate important aspectes of the alternate bearing behaviour of cv. Boskoop. But also for this approach, further studies are needed to come to robust, practical recommendations. The approaches are discussed for their pros and cons.