Apple crop thinning by tree shading

Shading with nets of 2 m and 3 m width respectively, which reduce the photosynthetic active radiation by 74 %, lead to successful fruit thinning of apple trees. Such a thinning method could be interesting for organic as well as for integrated production. Field trials in 2006 and 2007 with the cultivars Golden Delicious, Elstar and Topaz showed, that this thinning method regulated the crop load to the necessary extent and the achieved fruit quality is acceptable. However, cultivars respond differently to the length of shading. Three days of shading reduced fruits per 100 flower clusters to a satisfactory extent for Golden Delicious (if shading after 19, 26 and 33 days after full bloom) and Topaz (if shading after 19 and 26 days after full bloom). For Elstar, seven days shading at 25 days after full bloom resulted in a good thinning effect. Flower counts in the following year showed a reduction in alternate bearing for the shaded trees. The results obtained demonstrate that the response of the method to meteorological conditions seems to be surprisingly low. Date and length of shading seems to be more important. Practicability of the method in farmers’ orchards has yet to be improved, however. Net installation is still too costly and time-consuming, therefore easy to handle and cheap methods must be developed. The European ISAFRUIT-project made these studies possible by providing the necessary international collaborative research network and the funding.