Plant Growth Regulator Use in Cotton Production

Several folks throughout the state have began applying plant growth regulators to their cotton crop and many more will likely start over the next couple of weeks.  Although plant growth regulators have gotten exponentially cheaper over the past 25 years, the basic chemistry of these products has remained unchanged.  First and foremost, do not use plant growth regulators with the goal of increasing yield.  Although research data is available showing yield increases from plant growth regulator application, just as much or more research data is available showing no yield benefits from plant growth regulator application.  The primary reason for plant growth regulator applications should be management of vegetative growth.  Managing vegetative growth provides several key benefits including:  increased pesticide penetration into the crop canopy, increased efficiency of harvest aid applications, and increased picker efficiency.

When making plant growth regulator applications several factors should be considered.  The variety to which these applications are being made should be heavily considered.  As everyone knows, some varieties display more aggressive growth than others.  As such, overapplying plant growth regulators to less aggressive varieties can potentially cause yield losses.  Productivity of the soil in a given field should also be considered.  Soils that are fertile, well drained, have high levels of organic matter, etc. have the tendency to produce rank cotton and thus, increased plant growth regulator application rates may be warranted in order to keep the crop in that field at a manageable height.  Irrigation capability should also be considered as having the ability to apply irrigation can help overcome over application of plant growth regulators.  Product selection is at the discretion of the person paying the bills.  Research at Mississippi State has shown no differences in terms of limiting vegetative growth (or yield for that matter) between products when used at equivalent rates.  Having said that, if you prefer to use the cheapest reputable product available, by all means do so.  If you would rather use lower application rates and thus handle less material with a given product that is ok as well.  However, do not select a product based on purported benefits over another in terms of limiting vegetative growth, yield, or fiber quality.  Our research has shown that most products perform in a similar manner which makes whatever choice you make the right one.

Examine the internode length between the fourth and fifth node downward from the terminal to determine how well your crop is growing.  If these internode lengths are 2″ or less you may consider holding off on plant growth regulator applications.  However, if you have internode lengths of 3″ or greater you should make an application in order to prevent that crop from getting excessively tall.  Rates should be adjusted based on cotton variety, internode length, and growth conditions in the days following the application.