growth regulators, synthetic substances which act on vines like hormones to regulate their growth and development. A synthetic auxin, 4-CPA, has for example been used to improve fruit set. Synthetic gibberellins have been used to increase berry size, especially for the seedless sultana, and a synthetic ethylene-releasing compound termed ethephon can be used to hasten grape maturity and enhance colouration in particularly cool climates. More recently applied to viticulture, hydrogen cyanamide encourages early and complete budbreak, which can be useful for tropical viticulture. These chemicals are mostly used for table grapes and their application to both table grapes and wine grapes is regulated by rules governing the use of agrochemicals. Some hormones effective on grapevines—abscisic acid and cytokinins, for example—have not been produced commercially for use in the vineyard.
