Differential Response of Cotton Varieties to Plant Growth Regulator Applications

The application of plant growth regulator chemicals have become common practice in cotton production across the cotton belt.  The objective of this  study was to compare and contrast  yield performance and crop development  of experimental and commercial cotton varieties in South Carolina in response to various plant growth regulator programs.   Replicated field studies were conducted in 2008 and 2009 at the Pee Dee Research & Education Center located in Florence, SC.  Three plant growth regulator programs and ten cotton varieties were arranged as split-plots in a randomized complete block design with four replications.  Plant growth regulator programs consisted of:  1) untreated,  2) a standard program, and 3) an aggressive program.    The aggressive PGR program (3 sprays of 40 oz/a total) reduced lint yield 7% compared to a more standard PGR program (2 sprays of 24 oz/a total) or the untreated.  PGR applications appeared to change the internal partitioning of dry matter within cotton bolls.  The use of Pentia in this study reduced gin turnout and micronaire, and increased fiber length.  The use of Pentia reduced plant height, the number of nodes, and the height:node ratio, decreased the first fruiting branch, and increased the number of bolls produced between nodes 6 and 10.   No PGR x variety interactions were found for any of the parameters measured in this study, with the exception of seedcotton.  Seedcotton production was reduced 21% with DPL 0912 B2RF by the aggressive use of PGRs during the growing season compared to the untreated plots.  Likewise, seedcotton production was reduced 15% with DPL 143B2RF by the use of an aggressive PGR program compared to a more standard PGR program.   Seedcotton production was increased 14% with DPL 555BR and DPL 0935B2RF  by the use of a standard PGR program during the growing season compared to no PGRs applied at all (untreated).