Effects of growth retardants on Vitis vinifera L.

Four growth retardants, CCC, Phosfon-D, Alar and CO 11, have been tested on Vitis vinifera over five seasons. Applications have been made by vine spraying or cluster dipping. Spraying with CCC resulted in darker green leaves, shortened internodes, retarded tendrils, increased numbers of inflorescences differentiated on lateral shoots, greater berry set and smaller berry size. Not all of these effects occurred together, the most frequent effects being on tendrils and berry set and size. Cluster dipping affected berry set and size in the same way as vine spraying but had no effects on other organs. Set was increased more than 20 per cent in about half of the 46 experiments. At the same time, berry size was reduced by about 10 per cent so that cluster weight or yield was only increased by more than 20 per cent in two-fifths of these experiments. Comparison of concentrations of CCC between 10 and 1000 ppm showed, in general, an increasing effect on set with increasing concentration. The most effective time of treatment was one to three weeks before anthesis; timing does not appear to be critical. Phosfon-D, like CCC, increased setting but caused a severe patchy chlorosis of leaves. Alar and CO 11 were, in general, without effect in these experiments.