Studies were conducted to generate data on the effects of mepiquat chloride (PIX^®) at different temperatures on several physiological processes in cotton (Gossypium hirsutum L. cv. ST 825) for the purpose of simulation modeling. These experiments were conducted in naturally lit controlled environment chambers with PIX^® levels of 0 and 49.42 g ai ha^-1 and day/night temperatures of 20/10, 25/15, 30/20, and 40/30 C with a CO₂ concentration of 350 µI 1^-1.

Mepiquat chloride decreased the leaf area of the growing leaves and decreased the specific leaf area up to 22% throughout the cotton canopy at all of the temperatures. A 50% decrease in the increments in plant height was observed at the lower temperatures. The data showed a decrease in internodal length, number of main stem nodes, and branches when treated with PIX^®. At the higher temperature regimes gross photosynthesis increased when treated with PIX^®. The data were used to develop a subroutine to simulate the growth and photosynthesis of PIX^®-treated cotton crops.

The new subroutine PIX^® is incorporated in the cotton simulation model, GOSSYM, which simulates the effects of PIX^® as a function of canopy temperature and PIX^® concentration. The cotton simulation model GOSSYM with its new PIX^® subroutine is presently being used for cotton crop management throughout the cotton belt.