ABSTRACT

DP 555 BG/RR is a high yielding mid to full season variety that exhibits above average growth potential during the flowering period. Growers familiar with the variety have been more inclined to use MC treatments to control any excessive vegetative growth that might occur. Much of the US cotton belt is reliant on rainfall to sustain growth during the flowering period, hence, future growth is not always predictable. MC yield response trials using DP 555 BG/RR were conducted from Texas to North Carolina in 2003 on research farms as well as grower cooperator fields. All but one of the 14 trials were conducted in 2003. All locations had a treatment comparison of control and MC application estimated to achieve 15 ppm in plant tissue following application. Several locations had additional MC treatment rates such that there were 22 total MC treatments compared across 14 environments in this study. Plant monitoring data were collected during and at the end of the season to quantify treatments. Regression and multiple regression analysis were used to determine the relationship between plant monitoring variables and MC response. Average IID early (IID cotyledons to 8) was positively associated with MC response. Values less than 1.3 inches per node generally had no yield response to MC application while values above 1.5 had a consistent response. Average IID during the late squaring to early flowering stage (IID 8 to 14) showed a low probability of response to MC at values at or below 2.5 inches per node while values at or above 2.7 inches per node had a high probability of MC response. A total of three fields had good early growth, but limited growth during the middle of the season, but still had slightly positive MC responses. Many of the trials had better than average mid to late season growth due to favorable rainfall throughout many of the test locations resulting in an average yield increase from MC treatment to achieve 15 ppm MC at the first application date. Trials will be continued in 2004 with in an attempt to obtain additional data under conditions of good to excellent early growth followed by mid or late season stress to further document DP 555 BG/RR response to MC applications.