Although the early-planted cotton production system offers the potential of improved lint yield, production techniques need to be optimized to ensure consistent yield enhancement. The objectives of this study were to determine how different seeding rates and application rates of mepiquat-type plant growth regulator compounds (PGR) affected cotton growth and production under early planting conditions. A field study was conducted under early planting conditions from 2001 through 2004 using four cotton cultivars (PM 1218BR, STV 4691B, STV 4892BR, and DPL 555BR) and four seeding rates (7, 9, 11, and 13 plants m-2). Depending on the year, half the plots were treated with either mepiquat chloride or mepiquat pentaborate (plus PGR), while the remaining plots were untreated (no PGR). Dry matter partitioning, canopy light interception, bloom counts, lint yield, yield components, and fiber quality data were collected throughout the experiment. When PGR was not applied, leaf area index (LAI) increased as the seeding rate increased, but the LAI plateaued at 11 plants m-2 when a PGR was applied. When a PGR was applied to the crop, plant height was reduced 9% and specific leaf weight was increased 4%. Plants treated with a PGR produced more flowers early in the season, and the untreated control plants produced more blooms later in the season. The potential for earlier maturity of plants treated with a PGR was also reflected in the reduced nodes above white bloom (NAWB) data relative to the control plants. No yield response was observed from PGR application, but the lowest seeding rate (7 plants m-2) had 5% lower yield than any of the other seeding rates. Few fiber quality differences were detected among PGR application rates or seeding rates. The longer growing season associated with the early planting system allowed late season flowers on the control plants to develop into mature open bolls and resulted in equivalent yields between the control and plants treated with a PGR.
