ABSTRACT

PGR-IV is a multiple-entity plant growth regulator that can purportedly alter the plant hormone balance leading to increased boll set and retention. This study was conducted to evaluate rates and timings of PGR-IV on boll distribution, lint yield, and fiber quality. Field studies were conducted in 1990, 1991, and 1992 in which lint yield and fiber quality were measured each year, and boll mapping was performed in only the last two years. Four treatments were used in the study: 1) untreated control, 2) PGR-IV 8 oz/A at early bloom, 3) PGR-IV 4 oz/A at pinhead square and early bloom, and 4) PGR-IV 2 oz/A at pinhead square, early bloom, and early bloom plus two weeks. All treatments were made using broadcast applications. No significant differences (á=0.05) for boll distribution, lint yield, or fiber quality were observed for any PGR-IV treatment or year by PGR-IV treatment interaction; however, lint yield differed at the á=0.10 level of significance. The 4 oz/A rate of PGR-IV applied at pinhead square and early bloom produced more lint than the 8 oz/A rate of PGR-IV at early bloom and the control (1629, 1533, and 1500 lb/A, respectively). Several trends for numerical differences were observed. The control plants had numerically greater average internode length (0.1 cm) and more reproductive nodes (1.0) than PGR-IV treated plants, which may be an indirect effect of PGR-IV's influence on boll distribution. Numerically a greater percentage of total bolls occurred on the first two fruiting positions (4%) and the lower ten reproductive branches (4%) of PGR-IV treated plants compared to the control. PGR-IV treated plants had fewer bolls per plant (1.0), but produced more lint (81 lb/A) than non-treated plants.

Micronaire was numerically greater for PGR-IV treated plants compared to the control (4.5 versus 4.3). Although not significant, these results suggest that PGR-IV has a positive effect on many plant growth and development parameters.