Investigations on the cause and control of alternate bearing of Satsuma orange trees. VII

Abstract

1. It is very interested to know the effectiveness of fall and winter sprays of potassium and phosphate on the flower bud formation of Satsuma orange trees.Satsuma orange trees of 19-and 60-year-old, nearly uniform size, growth, and bearing habit and of medium growth were used. The rootstocks were Poncirus trifoliata.1 or 0.3 per cent solution of KH2PO4 were sprayed from the middle of October to the end of January.The number of flowers, represented as per cent of the number of nodes, increased by the sprays on the harvest time of Satsuma orange in November and December.The more effects were observed on the shoots of weak growth by sprays of KH2PO4 than the shoots of medium growth.From chemical analysis of the shoots sampled in the following January, it was shown that the sprayed shoots contained less nitrogen and much more carbohydrates than the unsprayed shoots.2. The oil-emulsion has been used as the common spray material for the control scales and other insects and mites. However, it has been also found that there are some deleterious effects on the physiology of the orange and flower bud formation by the oil emulsion spray.3. Three per cent of oil emulsion diluted from 60 or 95 per cent of the machine oil was used in the experiment.a) The number of flowers, represented as per cent of the number of the nodes decreased on the shoots of medium and weak growth, which was sprayed on January 15 and February 25. There was no effect on the flower formation by the sprays at the time of the flower differentiation in March.b) Oil emulsion was sprayed over the halves of the main branches of each tree on December 24 and January 24. The lateral shoots developed from the sprayed and non-treated branches were defoliated once a month November to February.The number of flowers on the defoliated and sprayed branches were 8 to 18 per cent less than those of the defoliated and non-treated branches.The number of flowers on the shoots defoliated on November were the least.