Omenien putoamisen vähentämisestä ennen sadonkorjuuta ja sen aikana

Authors

• Jaakko Säkö Puutarhantutkimuslaitos, Piikkiö

DOI: https://doi.org/10.23986/afsci.71507

Abstract

The preharvest and harvest drop of apples often causes considerable losses to the fruit growers. The early summer varieties are especially liable to drop, but dropping is also found to be a common occurrence among many autumn and certain winter varieties. In a few varieties, such as Filippa, the fall may be quite rapid. In most varieties, however, it happens graduelly increasing during the time the apples approach their full maturity. On the other hand we also know apple varieties, which keep their fruits well after reaching maturity. This is the case e.g. with Huvitus and Lobo, which are grown as standard varieties in Finland. Spraying with growth regulating substances in order to delay the preharvest drop of apples has been a common practice especially in the USA and Canada. The chemical first used for this purpose was α-naphthaleneacetic acid. However, in this respect great progress was made when EDGERTON and HOFFMAN (4) found that 2,4,5-trichlorophenoxypropionic acid (2,4,5-TP) was an ideal chemical for the control of the preharvest drop of Mclntosh apples. Later such sprays have been applied succesfully to several apple varieties (3, 5, 10, 11, 12). In 1958 experiments for controlling the preharvest and harvest drops of some apple varieties with 2,4,5-TP were made at the Department of Horticulture, Piikkiö. The following varieties were tested: Bergius, Sävstaholm, Melba, Atlas, Wealthy, Åkerö and Antonovka. The applications were given 21—33 days before the harvest, both by dilute (20 ppm) and by concentrate (80 ppm) sprays. Furthermore the effect of Tween 20 (polyoxyethylene sorbitan monolaurate) on 2,4,5-TP was studied. Tween 20 has been used as an additive to increase the effect of α-naphthaleneacetic acid in the thinning of apples (7). The results are shown in Tables 1 and 2, and in Figs. 1 and 2. 2,4,5-TP has proved very effective in delaying preharvest and harvest drops in all the varieties mentioned here. The concentraded sprays (80 ppm) have been superior to the diluted (20 ppm) applications. A concentration of 80 ppm did not result in picking difficulties at harvest. Despite the higher concentration, the low volume application supplied only about 50 per cent of the 2,4,5-TP applied per tree in the dilute spray. The additive Tween 20 in concentrations of 0.125 and 0.25 per cent increased the effect of 2,4,5-TP in the Wealthy and Antonovka varieties, whereas on the Åkerö variety it did not have any marked effect. In all the varieties mentioned the application of 2,4,5-TP resulted in a better colour of the apples. This was particularly pronounced in the Melba and Atlas apples. The treated Antonovka apples were also decidedly more yellow at harvest time than the apples from the check trees.