Timely Defoliation to Maximize Fiber Quality Potential

The most critical component for producing high-quality cotton is variety selection. The genetic makeup of a variety can play a large role in fiber quality.

Fiber quality develops throughout the entire growing season, and certain production practices can help protect the fiber quality potential of the variety planted. Proper use of harvest aids prior to harvest is one management step in cotton that can impact both yield potential and fiber quality. Cotton defoliation is the application of harvest aids to prepare the crop for harvest. Defoliating a crop or applying boll-opener products too early or too late will have a negative impact on yield potential and fiber quality.

When deciding to defoliate cotton, carefully consider crop maturity and field and growing conditions prior to making applications. Understanding the growth characteristics of the variety planted can also help with defoliation timing. A desiccant may be applied after defoliants and boll openers to help speed up the plant drying process. Boll openers may also be used to enhance activity. Boll openers increase ethylene production within the plant to hasten opening and accelerate drying.

When applying a defoliant, desiccant or boll opener, many factors must be considered. It is advisable to check your university recommendations for a general cotton defoliation strategy. One or more of the following can help determine when to defoliate the crop:

Percentage of Open Bolls

This is a widely used method based on the total percentage of open bolls in a field. The most common recommendation for defoliant application is when at least 60% of the bolls in the field are open. Again, it is advisable to check your university recommendations.

Nodes Above Cracked Boll (NACB)

This method is determined by locating the uppermost first-position cracked boll with visible lint and counting the number of mainstem nodes to the uppermost harvestable boll. Defoliation is generally recommended at 4 NACB.

Accumulated Heat Units After Cutout

Defoliation is recommended after 850 heat units (DD60s) have accumulated, which is typically after cutout or five nodes above white flower (NAWF). A drawback to this method is the amount of heat units required can vary by variety. This method also requires a determination for cutout, which can be different for every field.

Slice a Boll

Assessing boll maturity can be done by cutting bolls and observing the seed and fiber within. Choose the uppermost boll that has a chance of contributing yield, and make a cross section of the boll with a sharp knife. Generally, this boll will be located four to five nodes below the terminal, depending on end-of-season stresses. Bolls are mature when they are difficult to cut and a cross section of the seed reveals folded cotyledons, absence of jelly and darkened seed coats.

There is as much art as there is science in determining when to defoliate a cotton crop, and best practices can help preserve both yield potential and fiber quality.

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