Control of Vegetative Growth of Stone Fruits with Paclobutrazol

Abstract

During the last decade, fruit growers in Chile have made dense plantings of many species of fruit trees to obtain early and high yields of quality fruit. Control of tree size has become the most important problem to many growers. Usually, heavy pruning in summer and winter is used to keep the tree within a certain space and to maintain a good yield of high quality fruit. This pruning is costly and often fails (1). There is a great need for dwarfing rootstocks in most fruit tree species. Good dwarfing commercial rootstocks are available for apples and pears, but few exist for stone fruits (6). Therefore, growth retardants are being tested to regulate the size of fruit trees (4, 6, 8-10). The growth retardant β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol) (PB) is being tested in Chile on peaches, nectarines, plums, apricots, and cherries since PB is the best known and widely tested product of this kind. PB and other growth retardants can induce effects either applied to the soil or sprayed on the foliage (2). When PB is applied to the foliage, the effect on the vegetation is faster than from soil applications, but is of short duration, and several foliar applications are needed to maintain growth retardation. Effects of PB, on stone fruits were studied through soil applications, because Chilean fruit growers wish to use the least number of sprays possible. In our trials, soil applications were made at flowering time. The formulation of PB used was a 25% flowable concentrate under the commercial name of Cultar. These trials are part of a 5-year study on gibberellin biosynthesis inhibitors. Results in tables and figures were recorded after the second year when maximum effects were expressed.