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Since 2005, Ethephon is registered for all apple cultivars in Switzerland. This agent can be applied at three phenological stages: flower «pink», petal fal» or at 8-12 mm fruit diameter (at least 14 days after flowering). The application rate is 0.3- 0.5 l/ha. Thinning effect depends on the temperature, optimal at 18-22 °C. Above 25 °C (risk of overthinning) or below 15 °C, Ethephon should not be applied. When used in combination with NAAm at petal fall, conditions for NAAm should be followed. The impact of Ethephon varies very much. On one hand the thinning effect may fail, on the other hand the risk of overthinning is higher compared to the usual agents NAAm and NAA. With the admission of Ethephon and the setting of three application stages, the thinning of a cultivar can be more adapted to the different growing stages. However, Ethephon application is to be considered especially for cultivars with thinning difficulties or alternate bearing as a supplement to NAAm or NAA. Ethephon is not recommended with Golden Delicious for its low impact and russeting stimulation.
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