PGR-IV is a new plant growth regulator from Microflo, Lakeland, FL, consisting mainly of gibberellic acid and indolebutyric acid, which has been reported to ' rove imp the growth and yield of cotton. However, inadequate information exists about the use of PGR-LV and its effect on the physiology of the cotton plant. The objective of this research was to investigate the ld of effects of PGR-IV application on the growth and yield cotton. Specific objectives addressed the influence of PGR-LV on leaf photosynthesis, square retention boll development, root growth and nutrient absorption to explain the physiological reasons for PGR-IV enhancing boll retention and yield. Field studies were conducted at Marianna, Arkansas, to study the effect of PGR-LV on early-season plant growth, photosynthesis, and components of yield. Greenhouse studies were conducted to determine the optimum rate and timing of applying PGR-LV. Growthroom studies were used to determine the effect of in-furrow application of PGR-LV on root and shoot development of cotton seedlings.

Application of PGR-LV @ 4 oz./acre to field-grown cotton at pinhead square and first flower resulted in a significant yield increase of 69 lbs lint/acre (+6.6%) compared to the untreated control. When an in-furrow application at a rate of 2 oz./acre was combined with the above foliar treatment, a yield increase of 189 lbs/acre (+17.9%) resulted. The yield enhancements were associated with increases in early-season plant growth, leaf photosynthesis two weeks after application, nutrient partitioning, and boll number.

Growthroom studies showed that the optimum timing of a single application of PGR-LV was in-furrow at planting, at the second true leaf or pin-head square stages of growth. Applications at these times had the maximum grow positive influence on dry matter, leaf area, and square retention. The optimum rate of PGR-LV was 2 oz./acre applied in-furrow at planting, and 4 oz/acre applied foliarly after the second true leaf, and at pinhead square stages.

Growthroom studies of in-furrow applications of PGR-LV at planting resulted in a dramatic increases in root length, root dry weight and the number of lateral roots per plant one week after planting. These differences were still apparent at pinhead square but to a lesser degree.

Conclusion, when PGR-LV is applied in-furrow at painting or at pinhead square and early bloom, growth ana seedcotton yield are improved. The increase was associated with increased photosynthesis and improved square retention resulting in an increased number of harvestable bolls and higher yields.