Plant Growth Regulator Use in Cotton

As blooms are beginning to appear, several calls have come in this week regarding PGR use in cotton.  While some folks have already made some early applications, others are holding off.  Similar to defoliation, albeit with somewhat less pronounced effects if overdone, managing vegetative growth in cotton with PGR’s does involve some art as well as science.  I prefer to let the cotton plant itself dictate when to make an application as opposed to an automatic application made in combination with a herbicide and/or insecticide.  However, keep in mind that several other factors must be considered.  First and foremost the variety you are looking at must be considered.  Everyone knows that some varieties are more aggressive than others and as such, requires more intensive PGR management.  A link is included below illustrating relative PGR needs of several varieties.  In addition, the land cotton in being grown on must be considered.  If the land is highly productive, drains well, has good fertility, has irrigation capabilities, etc. you will most likely need to be more aggressive with PGR applications compared to cotton grown on land that is non-irrigated, tends to hold water, etc.

In short, you will want to examine the youngest fully expanded internode on the cotton plant to determine PGR needs.  The youngest fully expanded internode typically occurs between nodes four and five downward from the terminal.  If the length of the space between nodes 4 and 5 (the internode) is greater than 2.5″, a PGR application should be considered.  In addition, look at overall plant height when determining application rates.  If you plants are at early bloom and are less than 24″ in height but the youngest fully expanded internode is greater than 2.5″, a PGR application is warranted although you may not want to be excessive with application rates.  If your plants are >30″ in height at early bloom and the youngest fully expanded internode is >2.5″ in length, you will likely need to increase PGR application rates.

Regardless of the strategy you use, keep the following in mind.  A tremendous amount of research has been conducted on PGRs in cotton.  It is universally accepted that PGRs are beneficial for managing vegetative growth.  Managing vegetative growth is beneficial for a number of reasons including increased penetration from insecticide and herbicide applications, easier defoliation, and increased harvest efficiency.  The water become murky with respect to PGR effects on yield.  Data is available supporting increased yields, decreased yields, and no effect on yields from PGR application.  Data indicates that in a long, favorable growing season, PGRs are of minimal benefit in terms of yields.  In shorter, more truncated growing seasons, PGRs may be of more benefit with respect to yield.  My advice is to use PGRs to manage vegetative growth and have minimal expectations for yield increases from PGR applications.

Cotton Management Guidelines