Development of a System for Determining Relative Plant Growth Regulator Requirements for Cotton Varieties in Georgia

Plant growth regulator (PGR) applications are often necessary in cotton to reduce vegetative growth and maintain a manageable crop.  However, PGR sensitivity varies widely among varieties and environments.  Some varieties need to be monitored closely and heavily managed while some are sensitive such that overuse may negatively impact yield.  Research in 2010, 2011, and 2012 investigated the response of various varieties managed with either no PGR applications or a heavy PGR regime which included multiple applications made pre-bloom and during bloom.  Growth parameters and lint yield and fiber quality were used to assess the growth potential of a variety and document the impact a heavy PGR regime has on development and yield.  From this data, a classification system was developed which grouped varieties in order to more adequately define relative PGR requirement of cotton varieties in Georgia.  Four classifications were utilized, from varieties which may require no PGR management up to varieties which will need to be heavily managed with multiple applications.  Varieties were grouped together based on similar growth patterns and response to PGR applications.  After examining data from 2010 and 2011, standard varieties were identified and utilized to compare new varieties in 2012 to more easily predict their PGR requirements.