As is the case in many years, the 2013 Georgia cotton crop is widely variable in terms of growth stage depending upon planting date.
Most of the early planted fields (late April to early May) are within the first couple of weeks of bloom, with several slightly later planted fields at various stages of squaring, and late planted cotton (early to mid-June) ranging from seedling to 4-5 true leaves.
Most of the double-cropped cotton was planted noticeably later than normal this year. Soil moisture has recently been adequate to excessive in most of Georgia’s cotton belt due to frequent and hefty rains. Effects have been variable with regard to growth and development. Many fields have been waterlogged which has noticeably slowed growth of younger cotton, while other fields of older cotton (near bloom or within the first couple of weeks of bloom) are currently showing signs of vigorous growth.
Due to wide variability in crop growth, we strongly recommend that growers make growth management decisions on a case-by-case and field-by-field basis, as opposed to a one-size-fits-all approach. When making plant growth regulator decisions, it is important to recognize the actual effects that mepiquat-containing PGRs have on the plant and how this may or may not benefit the grower.
Mepiquat-containing PGRs reduce the production of plant hormones called gibberellins or gibberellic acid. Gibberellins are natural plant hormones that are involved in cell expansion. When mepiquat is applied, the internodes near the terminal of the main stalk or on lateral branches (regions where elongation occurs) may not elongate to the degree that non-treated plants would.
This usually results in shorter plants, with more compact nodes. Most mepiquat-containing PGRs, with the exception of Stance, generally have similar effects on plant growth. When applied at similar rates (except for Stance), similar results should be expected. Stance contains a higher concentration of mepiquat than other mepiquat products, and also includes cyclanilide. This product is used at much lower rates than standard mepiquat products.
Some PGR misconceptions
It is important to understand what mepiquat-containing PGRs do not do, as there are some misconceptions out there. Mepiquat does not stimulate flowering and does not create more bolls per plant. At best, mepiquat may improve retention of some bolls, but it does not cause the plant to produce more bolls.
Lastly, and most importantly, yield responses to mepiquat are inconsistent at best….yields are improved in some situations, reduced in other situations, and in many cases, PGRs have no effect on yield at all.
So why use PGRs? Some of the more beneficial effects, again which may or may not occur, are improved fruit retention on lower nodes and earlier maturity (generally more beneficial to later planted cotton, and especially later planted irrigated cotton), improved harvest efficiency, reduced impedance of insecticides/fungicides/harvest aids, reduced boll rot and reduced lodging of plants (all of which in the right circumstances could potentially increase yield).
The likelihood of achieving one or more of these positive results greatly increases if the environment is likely to result in (or has historically and consistently resulted in) excessive vegetative growth. But even then, these results may or may not occur.
There are risks associated with mepiquat applications, especially when improper rates and/or premature application timings are implemented. Keep in mind that mepiquat should be used in a manner to prevent rank growth from occurring, but remember that plants still need to be tall enough to support an optimal boll load, thus an optimal yield.
An optimal plant height generally varies depending on the situation. This should be determined on a case-by-case basis and could be adjusted for other situations.
Growing season, weather affect PGR decisions
One other thing to consider in Georgia is the length of the growing season and weather as it relates to cotton maturity and fruit retention:
Most importantly, one should consider that our relatively high temperatures and high humidity create a situation where fruit retention can be an issue to consider, such that fruit retention on lower nodes may explain why the crop is difficult to control with PGRs.
It is also important to remember that conditions which occur during boll opening (especially in early planted fields) may impact the ability to harvest those bolls on lower positions, whereas boll rot can greatly impact the harvestability of fruit particularly those deeper in the canopy. These factors should be considered when attempting to decide the optimum plant height required to maximize yields.
Another somewhat unique factor with Georgia’s environment is the length of the growing season. Our conditions often allow for cotton to be produced much later in the season than cotton grown in neighboring states (especially those north of us) and consideration should be made when comparing PGR ideas and recommendations from those regions.
This is not intended to make Georgia growers weary of PGR recommendations from other states, but it can potentially explain differences in PGR philosophies in Georgia compared to other states.
We now are dealing with some newer varieties that tend to be earlier maturing than DP 555 BR with generally less growth capacity than that of DP 555 BR. The range of maturity and growth capacity is very wide among these newer varieties, with some varieties showing somewhat similar characteristics to that of DP 555 BR. It is important to familiarize yourself with these characteristics of the varieties you choose to plant.
When DP 555 BR was still widely planted, most growers began their PGR applications at the 8- to 10-leaf stage, which was generally followed by applications at or near first bloom and again 2 to 3 weeks later. This program was a more preventative-type prophylactic program that generally worked well for DP 555 BR, especially in irrigated fields, as this variety could consistently result in (and was likely to result in) excessive growth and extremely tall plants.
Most (but not all) of the newer varieties tend to develop a larger boll load slightly quicker than DP 555 BR, which can restrain terminal growth to some degree, therefore growers can be more reactive than proactive/preventative with PGR management in some situations, especially with the earlier maturing varieties.
Some of the earlier maturing varieties with less growth capacity may not need a pre-bloom PGR application in order to prevent excessive growth, and delaying these decisions until first bloom may allow for better growth management decisions.
Keep in mind that some of the earlier maturing varieties may exhibit vigorous or aggressive growth prior to first-bloom, however the growth rate may rapidly decrease once these varieties enter the bloom period when the rapidly developing boll load begins to retrain terminal growth.
Aggressive, preventative approaches for early maturing varieties may in fact prevent plants from reaching an optimal plant height in some environments thereby risking yield loss associated with inadequate numbers of fruiting sites.
For later maturing varieties with greater growth potential, especially in timely irrigated fields, a more aggressive preventative approach (which may include pre-bloom applications) may be necessary to prevent excessive growth, but a one-size-fits-all approach is no longer suitable.
For specific information on varietal impact on PGR decisions, go to www.ugacotton.com