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When making the decision to defoliate cotton, careful consideration must be made with relation to crop maturity, field conditions, and the environment. Cotton fiber quality and yield can be maintained by paying attention to maturity and understanding growth characteristics of a variety.
Benefits of proper cotton defoliation can include: reduction in the sources of stain and trash (leaves), increased harvest efficiency, quicker drying of dew, straightening of lodged cotton plants, increased potential for boll opening, and a reduction of boll rots.
Factors Affecting Defoliation—When applying a defoliant, desiccant, or boll opener, many factors must be taken into consideration for successful application. The use of cotton plant growth regulators (PGRs) during the growing season can influence the efficacy of defoliants. PGRs work to reduce vegetative growth and slow the development of new nodes, which can help plants mature early and prepare for defoliation. Boll openers may also be used in combination with defoliants to enhance activity. Boll openers increase ethylene production to hasten opening and dry out. If applied to cotton prior to maturity, micronaire and fiber length can be reduced.
Defoliation Application—Successful defoliation depends on leaf coverage by the chemical. Higher sprayer volumes may be recommended to achieve adequate coverage to all plant leaves. Volumes between 10-15 GPA are recommended for most situations.1,3 Recommendations for most defoliant applications include the use of flat-fan or hollow cone nozzles. These types of nozzles provide excellent spray coverage.4 Drift-reduction nozzles, while excellent at controlling spray placement, have been shown to decrease coverage within the crop canopy.
Timing Defoliant Application—There is as much art as science involved in making the decision to defoliate. There are several methods producers can use to determine the best time to apply defoliants:
No one defoliant or harvest aid, rate, or specific timing is the solution for every field. Selections should be based on prior experience, price, environmental and crop conditions, yield potential, and the value of the crop. Knowledge of the lint and growth characteristics of each individual variety is critical in finding the best harvest aid program, with respect to product and timing.
Defoliants do not contribute to cotton yield potential or maturity, but are chemicals used to remove leaves from the plant. It is also important to recognize that problems can occur from the use of defoliants. Once a cotton plant is defoliated, fiber and seed development can slow or stop. If cotton is defoliated too early, bolls may not mature, which reduces fiber quality and yield potential. Defoliants should be applied only when a cotton crop has reached the desired maturity for harvest.
1 Defoliation general discussion. 2014. Mississippi State University Extension Service. www.msucares.com. 2 Stichler, C., Supak, J., Hake, K., and Warrick, B. The proper use of cotton harvest-aid chemicals. Texas Agricultural Extension Service. L-5142 http://texasextension.tamu.edu. 3 Miller, D., Stephenson, D., and Kruse, J. 2012. 2012 Cotton defoliation guidelines for Louisiana. Louisiana State University Extension. Pub. 2927. http://www.lsuagcenter.com. 4 Siebert, J.D., Craig, C. Stewart, S., and Miller, D. Cotton defoliant efficacy: Effect of carrier volume and nozzle type. Louisiana State University and University of Tennessee. www.utextension.utk.edu. Fountain, C.D. 2012. Cotton defoliation. North Carolina State University Cooperative Extension. http://duplin.ces.ncsu.edu. Web sources verified 8/10/16. 130101013720.