Towards Grower-friendly Apple Crop Thinning by Tree Shading

摘要

Light management with shading nets, which reduce sunlight by 74%, might be anudalternative to chemicals commonly used for thinning on apple trees. To study the effect ofudshading on crop load and fruit quality, trials were conducted in field experiments with theudcultivars Golden Delicious and Elstar in 2006. Trees were either covered 25 days after fulludbloom (DAFB) with a net during three days, or until the peak of fruit fall, observed afterudseven days shading. Ideal time length for optimal crop yield was seven days shading forudElstar and three days shading for Golden Delicious. Alternate bearing could be decreasedudas flower initiation counts the following year showed. In both experiments, inner quality ofudfruit such as sugar and firmness showed good values at optimal shading durationudcompared with chemical + hand thinning. In 2007, a second field trial was conducted withudcultivars Golden Delicious and Topaz to study the time period for shading in further detail.udShading was done for three days at 19, 26 and 33 DAFB using two net types (three- andudtwo-meter-net width, covering the trees entirely or only down to 50 cm above ground). ForudGolden Delicious, shading after 19 and 26 days reduced fruits per 100 flower cluster to theudsame extent as with chemical + hand thinning. There was no difference between the twoudnet types. For Topaz, shading after 19 days showed the best results. Regarding innerudquality of both cultivars, only sugar content for Golden Delicious could be significantlyudimproved after 19 and 26 days shading. Further analyses are still under way (e.g. forudacidity).udThis study is part of an effort for increasing European consumption with fruit fromudsustainable production systems, the ISAFRUIT-EU-project.