The plant growth regulator, ethephon [(2-chloroethyl) phosphonic acid], was applied to pre-bloom cotton, Gossypium hirsutum L., (cultivar DES 119), in Mississippi (1988) and south Texas (1989). In Mississippi, the ethephon was applied at the rate of 0.6 lb (AI)/acre on plants 0, 3, 6, or 9 days following boll weevil, Anthonomus grandis (Boheman), infestation. Immature boll weevil mortality in abscised squares from ethephon-treated plants tended to be higher than from untreated plants, when the ethephon was applied shortly following initial weevil infestation. Nevertheless, weevil infested squares on ethephon-treated plants did not abscise any sooner than those from control plants.

In Texas, where ethephon was applied at rates of 0.3 or 0.6 lb(AI)/acre, flower counts revealed that ethephon-treated plots lagged behind control plots for about three weeks, but thereafter, a higher flowering rate was maintained in the ethephon-treated plots for the remainder of the growing season. Square abscission in the lower part (branches 4 to 10) of ethephon-treated plants caused a shift in harvested bolls toward the middle (branches 11 to 17) and upper part (branches 18-23). Boll weevil damage evident in open bolls tended to be higher in ethephon-treated plants, particularly on the lower and upper branches. Boll opening time was more compressed in the ethephon-treated cotton, and there was no difference in lint yield or quality between the treatments. The timing for once over harvest was near the same (about July 31) for the control and the 0.3 lb (AI) rate, but was delayed about one week for the 0.6 lb (AI)/acre rate. Severe boll weevil damage reduced yields in all treatments, but more so in the ethephon-treated cotton. In addition, once-over harvest of cotton treated at the higher rate may have been delayed due to loss of mid-season fruiting forms to boll weevils.