The indeterminate growth habit of cotton ( Gossypium hirsutum L.) forces producers to harvest more than once or to postpone harvest for several weeks. Ethephon (2‐chloroethyl phosphonic acid) causes immature bolls to open, resulting in a greater percent of the crop harvested at first harvest or in once‐over harvest. The objectives of this study were to determine the effects of ethephon on seedcotton yields and fiber quality relative to the physiological stage of maturity at treatment with ethephon. ‘Stoneville 213’ and ‘CAMD‐E’ were planted on three dates in 1980 and Stoneville 213 on four dates in 1981 in Calloway silt loam, a Glossaquic Fragiudalf. Ethephon was applied at 1.12 kg ai. ha −1 and compared with no ethephon treatment in 1980 when plants ranged from 19 to 62% opened bolls. Stoneville 213 ranged from 12 to 72% opened when treated in 1981. The statistical design was a split‐block, split‐plot of a randomized complete block with four replications. Ethephon significantly reduced seed cotton yield when applied to cotton with 48 to 62% opened bolls in 1980 but not when applied to cotton averaging 22% opened. In 1981, no consistent effects of ethephon on seed cotton yields were detected. Over years, ethephon applied to cotton with 12 to 25% opened bolls did not reduce seed cotton yields relative to application to cotton with 48 to 72% opened bolls. No consistent detrimental effects on fiber quality were detected for fiber from first harvest or from once over harvest.
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Smith et al. (1986) studied this question.