A cotton plant is an indeterminate perennial, and produces vegetative and reproductive growth simultaneously. PGRs, or Plant Growth Regulators, are synthetic plant hormones that can be used to balance vegetative and reproductive growth in cotton. When PGRs are applied, there is good potential for change in the plants energy allocation away from potentially wasteful vegetative growth. Generally PGRs keep developing cells from elongating, leaving the plants with shorter and more efficient internodes. This does not necessarily increase yield, but it does help keep the plant more compact and potentially more water efficient. Producers often make use of PGRs at the match head square stage to better prepare for expected hot and dry conditions latter during the growing season.
There are three types of growth hormones that PGRs can impact in the plant, gibberellins, cytokinins and auxins. Gibberellins are most closely related to vegetative growth and promote cell division and expansion. Most PGRs reduce the concentration of this hormone in the plant, and prevents the cells from elongating, leaving a more compact plant (1). This compact plant has the potential to be more drought efficient, and consume less water than it would if it were larger. These synthetic hormones can also alter where the plant tends to bear fruit, and can cause a more compact fruiting zone.
Plant hormones work in very low quantities, and since PGRs are synthetic plant hormones, they work in very low doses as well. Increasing the amount of PGRs early will not increase or lengthen their effects. As the season progresses, PGRs can be applied several times in the season, but they should never be applied to a stressed plant (2). If they are applied to a plant that is stressed later in the season, PGRs can push a plant to cutout and reduce its yield potential.
We are one of the few areas in the country that commonly uses cotton strippers instead of cotton pickers. A cotton stripper’s efficiency is at its maximum when the cotton height is below 36 inches. Another reason to keep our cotton shorter than 36 inches is that tall, rank cotton plants tend to produce too much late fruit or bolls with little hope of maturing before an average freeze date. This means we need to watch our cotton’s height a little more closely than other regions might need to. Latter in the growing season, the top five internodes on our blooming cotton fields ideally would average to be about 1 inch in length. If those internodes start getting larger than 1.2 inches long, it would be time to consider applying a PGR. Conversely, blooming cotton with internode lengths of 0.8 inches are already experiencing drought stress.
Applying blanket PGRs very early in the season is not uncommon, especially in this area. When the cotton reaches the match head square stage, many producers apply PGRs often mixed with a herbicide treatment in the effort to prepare for coming water stress latter in the growing season. Fields with PGRs applied this early may fare better when the latter stress and heat inevitably set in during boll set. Right now, our cotton has seen wind damage and has been exposed to some early hot and dry conditions, but few fields can be considered drought stressed yet. Even in this drought, it should be safe to apply PGR for good benefit as fields reach that minimal match head square stage.
Good Luck! Please call or come by the office if you have any questions. Thanks!
Written by Kate Harrell, Intern with the Plains Pest Management Association and Texas A&M AgriLife Extension – IPM, Hale & Swisher County.
1 http://www.caes.uga.edu/extension/irwin/documents/PGRPublicationUGA.pdf . Philip
Jost,Jared Whitaker, Steve M. Brown, Craig Bednarz. Department of Crop and Soil Sciences College of Agriculture and Environmental Sciences Cooperative Extension Service. Bulletin 1305-Date April, 2006. 6/26/13
2 http://agfax.com/2013/06/26/texas-cotton-plant-growth-regulator-considerations/ . AG
FAX Fields of Facts on June 26, 2013. 6/26/13