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At this point in the season, growth management options are limited. Fertility and PGR programs have stopped as they will no longer be effective or economical. However, in areas where irrigation is utilized, water stress can be used late in the season to manage regrowth and hasten boll maturity. Due to a fortunate difference in sensitivity to water stress between vegetative growth and boll development, periods of substantial water stress late in the season can be tolerated with little or no effect on yields. This may be especially true for vigorous varieties or delayed crops where the control of late-season vegetative growth is beneficial. It is also possible that reducing irrigation frequency late in the season will lower the humidity in the lower canopy, thus reducing boll rot.
While defoliation does not necessarily mature a crop, a good harvest aid program can help mature crops at the peak of quality. The way a crop has been managed with fertility, PGRs, water, etc. affects defoliation. While defoliation practices differ by region, the timing of harvest aid programs and the components which need to be considered are common.
Growers can use scientific means of timing defoliation in tandem with information on
the number of acres
harvesting equipment can
cover daily to help stagger harvest rather than
defoliating entire farms at the same time. The foremost
means of determining crop readiness is nodes above cracked boll (NACB). Timing defoliation with NACB can
help maximize yields and quality.13;10;
Since growth and maturity are not uniform in most cotton fields, it is best to sample the area that is least mature since it will set guideline for harvest aid timing. A total of 20 plants randomly selected from the least mature area of a cotton field should be examined.
Selection of the most efficacious harvest aid chemicals depends on many factors — both within the plant and related to the weather.
For good defoliation to occur, cotton should be low on moisture and nitrogen. This balance is exceedingly difficult to reach since, in the case of nitrogen, this depends on application rate and boll load. When nitrogen fertilizer was applied, the total boll load was not known, only anticipated. Some growers use petiole testing for nitrate-nitrogen late in the season to schedule fields for defoliation. This method allows fields to be ranked in a relative order so the field which will be ready first can be prioritized for defoliation.
Weather also has a major impact on defoliation. Defoliants and desiccants are herbicides that when applied at appropriate rates will help prepare cotton for harvest. The weather, especially the temperature, has a large impact on the efficacy and performance of the defoliant. As temperatures increase, the activity of most defoliants also increases. Local experience is the best indicator of which defoliants will work best in each field.
This article is from the Cotton Management Guide, a publication with year-round advice on managing high-yielding cotton. Download the Deltapine Cotton Management Guide now or sign up for new content to be delivered to your email each month.