Journal of the Japanese Society for Horticultural Science
Online ISSN : 1880-358X
Print ISSN : 0013-7626
ISSN-L : 0013-7626
Studies on fruit (blossom) thinning of apples by hormone sprays. II
Thinning effects on Jonathan and Delicious group varieties
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1956 Volume 25 Issue 1 Pages 54-58


The further experiments of NAA sprayings on apple varieties (Jonathan, Delicious, Starking, Richard, and Golden Delicious) were carried out at the Economic Farm of Iwate University in 1953, to find out the best stage of spraying and the optimum concentration of NAA for fruit thinning and to know the effects on the leaves.
The results obtained were as follows.
(1) The optimum concentrations of NAA were:
10 ppm…… for Jonathan, Delicious, Starking and Richard
20ppm…… for Golden Delicious (further experiments needed)
The best stage for spraying was about one or
two weeks after full bloom as in the previous report.
(2) The effects on the leaves were different among the varieties. “Epinasty”, a special phenomena of hormonal effect, appeared as soon as NAA was sprayed, but disappeared after one week. It was probable that NAA was absorbed through the leaves, then caused the fruit drop, because the spray on the leaves exclusive was as effective as the one on both fruits and leaves.
(3) It was found that the chemical thinning of Jonathen, Delicious, Starking and Richard was promising, but hand thininng after the spraying was necessary.

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