ISHS Acta Horticulturae 463: VIII International Symposium on Plant Bioregulation in Fruit Production
THINNING RESPONSE OF ELSTAR APPLE TO THE FLOWER THINNER AMMONIUM THIOSULPHATE (ATS) |
| Authors: | J.M.T. Balkhoven-Baart, S.J. Wertheim |
| Keywords: | Malus domestica, apple, chemical thinning, ATS, ammonium thiosulphate, concentration, timing |
| Abstract:
There is a risk that thinning agents shall not be available for fruit growing in future. Chemical industries claim that costs for registration exceed profits. ATS (ammonium thiosulphate) being a fertilizer, is not yet considered as a growth regulator, but may act as a blossom thinner. In 1996, two trials were carried out on Elstar using ATS (a fine granulate with 99–100% a.i.) in 2 (0.5 and 1.0%) or 4 (0.5, 1.0, 1.5, 2.0%) concentrations applied one day after full bloom or 3 to 7 days later. Best results were obtained with 1.0% ATS sprayed shortly after full bloom. Higher concentrations proved very phytotoxic to flowers and leaves, whereas 1.0% ATS caused acceptable leaf damage. Size grading showed that concentrations higher than 1.0% did not improve fruit size despite of heavier thinning. Fruit russeting was linearily related to ATS concentration. The increased russeting by high ATS concentrations may have been caused by the more vigorous shoot growth due to the heavy thinning and not by the product itself. | |
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