Chemical Control of Vegetative Growth in Citrus Trees by Paclobutrazol

Abstract

Paclobutrazol (PP333) [(2RS,3RS)-l-(4-chlorophenyl)-4, 4-dimethyl-2-(l,2,4-triazol-l-yl-)pentan-3-ol] sprays applied to ‘Minneola’ tangelo trees, at 500 or 1000 ppm, before the onset of summer flush, markedly reduced total growth, number of shoots, and internode length. Soil treatments (0.4 and 0.8 g per square meter) had only a small effect, probably because of the short time from application to flush inception. Sprays of Morphactin (an auxin transport inhibitor), at 250 and 500 ppm did not reduce growth, but rather enhanced it by increasing the number of emerging shoots. The spring flush of the same trees also showed effects of paclobutrazol soil treatments, whereas other treatments were not different from control. Paclobutrazol sprays on comparable ‘Minneola’ trees just before the spring flush also reduced this growth. Paclobutrazol may become a tool for the control of vegetative growth of mature citrus trees.