What it is and why it’s important.
- Cutout and blooming out the top are often confused as the same growth stage.
- At cutout there are still many potential fruiting sites to be developed, and the timing of cutout is often used as a gauge of the fruiting window and yield potential.
- Blooming out the top signals the end of the fruiting period at which point flowers are present on the uppermost fruiting sites at the terminal.
The timing of cotton reaching cutout can be a critical factor for decisions regarding inputs and crop management, although this growth stage is often misunderstood or misidentified.
Cutout and the term “blooming out the top” are often used interchangeably to describe cotton near the end of the blooming period. However, these are two distinctly different growth stages in regard to the timing of their occurrence and crop status.
Cutout in cotton is reached when there are 5 nodes counting down from the terminal to the uppermost first position white flower, or the terminal is 5 nodes above the uppermost first position white flower (5 NAWF; Fig. 1).
First position refers to the fruiting site that is closest to the mainstem on the fruiting branch, with node referring to the point where a fruiting branch connects to the mainstem (Figure 2).
In general, when the cotton plant is cutout, it has reached its capacity for supporting fruiting positions and will likely not development any further fruiting sites that will result in harvestable bolls in addition to the fruiting sites already present (the squares that have already formed on fruiting branches above the uppermost white flower).
In other words, at cutout there may be up to of 7 or more fruiting sites (squares) in addition to the uppermost white flower and these can develop into harvestable bolls as long as adequate water and heat are available. However, there will be no development of additional fruiting sites that will result in harvestable bolls beyond what is present on the plant at the time of cutout.
Eventually the white flower will reach the terminal signaling the end of the flowering period. At this point the crop is “blooming out the top” and white flowers are present at the very top of the plant (NAWF 1 or 0; Fig. 3).
When cotton has reached this stage, there are no further nodes available to support fruiting sites and the plant is solely focused on developing and maturing the bolls and few remaining flowers into harvestable bolls.
What does cutout mean from the plant’s perspective? The plant is supporting a developing fruit load and is supplying the squares, blooms, and bolls with the resources needed to develop a mature, harvestable boll. Although the demand for water will start declining after peak bloom and as bolls mature, the plant will still require enough water to avoid stress, as well as heat units, to ensure the full maturation of all the fruiting sites.
Even though the crop is finished developing fruiting sites, proper management of both the crop and inputs is still necessary to optimize yield. In cases where the water supply is adequate, or if a fruiting gap (due to aborted squares or bolls lower on the plant) exists, the crop can stay at 5 NAWF for an extended period of time before the white flower reaches the terminal.
On the other hand, we often observe cotton in the Texas High Plains begin the flowering period at or close to 5 NAWF, most often in dryland scenarios. In these situations, it is difficult to extend the fruiting period as the crop has likely already experienced some sort of stress.
The flowering period will likely be abbreviated and fruit retention will be key to optimize yield in these challenging conditions. A more detailed description of cutout and scenarios where the cutout period can be abbreviated or extended is provided by this Cotton Physiology Today article.