Agricultural Applications of Ethephon

Abstract

Physiological effects on plant growth caused by the plant hormone ethylene have been noted for many years. More than 100 years ago, workers noted that illuminating gas or broken gas mains had deleterious effects on surrounding trees or plants. It was not until the 1960s that scientists documented that plant growth may be manipulated by applying ethylene. Some of the biological effects since noted include premature defoliation, fruit maturation ripening, induction of flowering, stimulation of sprouting or germination, and shortening of plant height. These effects are noted on a wide variety of agricultural crops, including vegetables, field crops, tree crops, and ornamentals. Ethylene is a gas and dissipates rapidly, and, thus, does not lend itself to field application. In the 1960s, the product ethephon [(2-chloroethyl)phosphonic acid] was developed. When taken up by the plant, ethephon is converted to ethylene in the cells and becomes available for physiological interactions. Because ethephon precipitates a wide variety of biological reactions, application technology becomes extremely important. Factors such as plant growth stage, plant stress status, plant foliage spray coverage, ethephon rates, and environmental conditions determine the responses obtained. An example is provided by processing tomatoes, where the desired response is to maximize fruit maturity enhancement and minimize premature defoliation—both ethylene responses. We have selected five agricultural applications of ethephon as examples of how plant growth may be altered. These are: increased boll opening in cotton; enhanced pistillate flower induction in hybrid squash seed; accelerated fruit maturity in processing tomatoes; enhanced hull splitting in walnuts; and reduced lodging in wheat. Each of these applications, and others, are common in California agriculture. Brevity necessitates providing only a summary of relevant applied research activities, which are not intended to be complete or thorough. Details on specific ethephon applications may be obtained from that particular researcher.