Two field tests were conducted in 1992 and four tests in 1993 in the San Joaquin Valley of California, to evaluate the effect of PGR IV on upland (Gossypium hirustum) and pima (G. Barbadense) cottons. All tests were field scale in size and employed plots of either eight 30 inch rows, or six 38 inch rows, by the length of the field, replicated five times. PGR IV treatments included at planting applications, and foliar applications, with and without pix. Leaf petiole samples were collected three times during the growing season and analyzed for nitrate nitrogen, phosphate phosphorus and potassium. Plant monitoring was conducted at three stages of growth to determine effects on fruit set and retention and plot yields were taken.

There was a trend toward more vegetative bolls and more second position bolls as a result of PGR IV applications. One test had significant differences among yield means, and all tests had highest yields in the treatments in which PGR IV was applied at planting, at first square, at early bloom, and pix at 10 days after square, or when pix was applied at early bloom.