A two-year study was conducted to generate a database on the effects of ethephon (PREP) and temperature interactions on several physiological processes in cotton (Gossypium hirsutum L. cv. DPL-50). Cotton plants were grown outdoors in pots at the nursery site of the USDA-ARS Crop Simulation Research Unit, Mississippi State University. At boll opening, nine plants were moved from the nursery to the sunlit temperature controlled growth chambers and arranged in three rows with 0. 66 m row spacing and nine plants per m². The air temperatures in the canopy were maintained at 15/5, 20/10, 25/15, 30/20 and 35/25 C day/night and ethephon was applied at rates ranging from 0.0 to 2.24 kg/ha.

At the appearance of the first flower, flowers were tagged, and starting at the first boll opening, all bolls were tagged to calculate the time from flowering to boll opening. Data were also collected on leaf abscission, fruit abortion, main stem growth and numbers of main stem nodes. Leaf water potentials were measured at frequent intervals throughout the experiment.

Ethephon decreased the ages at which bolls opened and the effect was more significant at higher temperatures. Increased defoliation was observed with both increased rates of ethephon and higher temperatures. A 300% increase in canopy defoliation occurred due to ethephon at 35/25 C. Immature fruit drop was significant at all temperatures with increased ethephon levels. The data from these studies also indicate that moderate ethephon levels increased vegetative growth. However, at higher levels of ethephon, growth was inhibited. The data were used to develop a new subroutine, PREP, for the GOSSYM/COMAX program. This subroutine simulates the plant processes as a function of ethephon rates and crop canopy temperature. However, for some plant processes leaf water potential was also used as a controlling factor. The cotton simulation model GOSSYM, with its new PREP subroutine, is presently being used for cotton crop management throughout the Cotton Belt.