Via Jared Whitaker in the 2015 Cotton Production Guide:
The best “growth regulator” for cotton is good, early fruit set and retention, as this will generally deter excess vegetative growth. Therefore, nitrogen levels, soil moisture, insect control, plant population, and crop management influence the cotton plants’ ability to balance vegetative and reproductive growth.
As a management tool, growth regulators containing mepiquat are specifically used to reduce vegetative growth.
Trials conducted in 2010 suggested that Stance applied at appropriate and recommended rates (usually 2.5 to 3 oz/a depending upon growth stage) may have milder effects on plant growth than the commonly used rates of other mepiquat-containing PGRs. Therefore, Stance may reduce risks of severe stunting due to hot or dry weather following application, especially for early maturing varieties or varieties that generally portray less aggressive growth.
Currently UGA data indicates that all mepiquat-containing products should be used at the same rates and timings, with the exception of Stance. The use rate of Stance recommended by Bayer CropScience is 3 oz/A in all situations. This rate may be lowered to 2.5 oz/A if the first application is made prior to, or at the initiation of squaring.
Even though mepiquat has been available for over 25 years, questions persist about how to use the product.
Factors that must be considered when determining when and how much mepiquat to use include: (1) stage of plant growth, (2) rate of plant growth, (3) pest control and (4) anticipated plant growth (irrigation, drought, fertility). Because of the many variables, hard and fast rules regarding the rate and timing of mepiquat are not appropriate. Fields vary in growth. Weather varies by year/location, and thus, recommendations must be flexible