The plant growth regulator, ethephon (2-chloroethyl) phosphonic acid], was applied to cotton Gossypium hirsutum L., during early season mid-june; pre-flowering) in the People's Republic of China (1984) and in Stoneville, MS (USA) (1987) using rates from 300 to 1000 ppm in 750 to 900 1 of water/ha. Ethephon caused square abscission and a rate response was evident. Soon after application the plants became flaccid, but they recovered within two weeks after application. Initial boll set was delayed by about 10 days, but the ethephon-stressed plants responded by fruiting at a higher rate than control plants and producing more harvestable bolls per plant. Bolls were generally heavier, there was a trend toward more uniform fiber length, and micronaire was higher. Ethephon treated plots yielded significantly more lint than control plots in two of four experiments. Ethephon-induced removal of squares on fruiting branches arising from mainstem nodes seven, eight, and nine caused a shift in placement of harvestable bolls to the middle and upper part of the plant as well as a proportionally higher number of harvestable bolls on nodes three and four of individual fruiting branches as compared to the control.

Early season ethephon application may have potential for increasing yield, improving lint quality, concentrating boll age (maturity), reducing boll rot, reducing plant height, and adversely affecting insect pest populations. However, plant fruit may be more vulnerable to insect damage during mid and late season and the optimal harvest date may be delayed. Intensive research on stress-induced assimilate movement in cotton plants is required to fully exploit and manage this phenomenon for more efficient production of cotton.