Studies on the control of alternate bearing in citrus. VI.

An investigation on thinning materials for Satsuma orange

Abstract

Thirty kinds of plant hormones and other chemicals were tested for their effectiveness in thinning flowers and fruits of Satsuma orange from 1950 to 1961. The materials were sprayed at the flowering time or at the young fruit stage, 3-4 weeks after petal fall, and subsequent fruit dropping, and, in some cases, fruit growth were examined.
1. MH showed thinning effect on heavy bearing branches and its phytotoxicity was comparatively slight. Its effective concentration was 0.15% when the plants were in full bloom and 0.3% at young fruit stage.
2. Growth regulating substances, such as 2, 4-D, 2, 4, 5-T, 2, 4, 5-TP, Amidthin and Gibberellin, showed no consistent effect for thinning in their lower concentration range, while in their higher concentration range they induced severe leaf injury.
3. As to insecticides, such as DN, oil and Parathion, their effective concentrations for thinning induced severe injury to leaves and fruits, and their safety concentrations showed no effect of thinning.
4. Herbicides and other materials, such as PCP, CMU (3-(p-chlorophenyl)-1: 1-dimethyl urea), CAT (α-chloro-4, 6 bis ethyl amino-s-triazine), CIPC, DCPA (2, 4 dichlorpropionanilide), Propazine(2 chloro-4, 6-bis isopropylamino-s-triazine), OED (polyoxyethylenedocosanol) and Dessicon (potassium isopropyl xantate), seemed to have no practical value as thinning agent.