Field experiments were conducted in 1991 at the Mississippi Agricultural and Forestry Experiment Station, Delta Branch, Stoneville, MS, the DuPont Field Research Station, Greenville, MS, and the University of Arkansas, Southeast Research and Extension Center, Rohwer, AR, to determine the impact of postemergence applications of DPX-PE350, fluometuron, and MSMA on cotton fruiting, maturity and yield. Trials were conducted in areas maintained weed-free and standard production practices were followed to insure optimum yields.

DPX-PE350 was applied at 1.5 or 3.0 oz ai/A pre-plant incorporated (PPI), preemergence (PRE), or postemergence-over-the-top (POT). POT applications were timed to occur when cotton was in the cotyledon to 1-leaf, 5- to 7-leaf, or pinhead square stages of growth. At Stoneville and Rohwer, a standard treatment of MSMA at 1.5 lb ai/A was applied postemergence at these same stages. Additionally, fluometuron at 1.0 lb ai/A plus MSMA at 1.5 lb/ ai/A was applied at the cotyledon to 1-leaf stage. All POT applications of DPX-PE350 contained a non-ionic surfactant at 0.25% V/V. A formulation of MSMA with surfactant was used, thus additional surfactant was not added to those treatments containing MSMA.

Mapping evaluations were conducted in July (early-season) and August (late-season) using a modification of the mapping procedures described by the National Cotton Council. In-season mappings included data on crop height number of nodes, node of first fruiting branch, number of white blooms, position of white bloom, number of squares, number of young bolls (<1 inch) and number of vacated positions. Mechanically harvested seed cotton yields were obtained at all locations. Phytotoxicity ratings were made periodically at the Stoneville location only.

There were no significant treatment effects at Greenville for any parameter studied. DPX-PE350 applied PPI, PRE, or POT at any rate did not adversely affect the number of nodes, number of white blooms, number of vacated positions, first fruiting branch or position of white bloom at any location. At late-season, the number of squares were reduced by DPX-PE350 at Stoneville. However, mapping data at a similar timing indicated an increase in square number due to DPX-PE350 at Rohwer.

At Stoneville, DPX-PE350 applied at the 5- to 7-leaf stage produced yellowing of cotton foliage and slight early-season height reduction which resulted in crop injury ratings of 11 and 25.% for the 1.5- and 3.0-oz rate, respectively. The 3.0-oz rate initially reduced the total number of nodes, but later mappings indicated no differences when compared to the check. Injury symptoms were transient and plants recovered without any subsequent effects on late-season fruiting or yield.

At Stoneville, when compared to the check, MSMA or MSMA plus fluometuron applied POT at the cotyledon to 1-leaf stage elevated the first fruiting node by approximately 2 nodes. Based on this, both of these treatments created a lag in fruiting, suggesting a delay in crop maturity. However, this delay in maturity did not adversely affect yields. The same fruiting response was not observed for MSMA at the Rohwer location. However, fluometuron plus MSMA applied POT at the cotyledon to 1-leaf stage resulted in a fruiting response similar to the Stoneville location. In addition, this treatment reduced early-season crop height and resulted in a yield decrease of approximately 15%.

In general, DPX-PE350 did not adversely affect cotton growth, fruiting or yield when compared to untreated plots. Some phytotoxicity was observed at later POT timings, but was transient in nature. POT application of MSMA or fluometuron plus MSMA produced noticeable effects on cotton fruiting which suggested a delay in maturity. Fluometuron plus MSMA applied POT at the cotyledon to 1-leaf stage reduced cotton yield at Rohwer but not at Stoneville.