Effects of Gibberellic Acid (GA3), Naphtalin Acetic Acid (NAA), Ethephon and Urea on Alternate Bearing Control in Kinnow Mandarin (Citrus reticulata Blanco)

Alternate bearing is a key factor in limiting citrus production. Chemical controls have proved to be the most effective solution to this problem. Two different experiments were conducted to study the effects of different growth regulators (GA3, NAA, Ethephon) and urea on alternate bearing control in Kinnow mandarin (Citrus reticulata). In the first experiment, GA3 at concentrations of 0, 25, 50, 75 and 100 mgl-1 were applied 3 times during late autumn and early winter 1993 on off trees. Flowers reduced as a result of GA3 application in the following spring but increased in the second spring. Best results obtained with 50 and 75 mgl-1. In the 2nd experiment thinning agents: NAA (0, 100, 200 and 300 mgl-1), ethephon (0, 100, 200, 300 mgl-1) and urea (0, 4, 8 and 12%) were sprayed to the trees on on-year, when the fruitlets were about 0.75-1 cm in diameter. The results indicated that urea had no effect however, both NAA and ethephon were effective on thinning of fruits and control of fruiting. Ethephon at 200 and 300 mgl-1, and NAA at 400 mgl-1 gave the best results.