Defoliation of cotton, Gossypium hisrutum L., prior to harvest is a critical step in maintaining cotton fiber quality.  However, defoliation is often referred to as more art than a science by industry leaders because of the complex interaction between cotton variety, defoliation products, and crop growth condition conditions.  The remnants of leaf material in harvested cotton can significantly increase leaf grade values and result in dockage to the producer.  In 2010 and 2011, multiple trials were initiated in South Texas to determine the impact of cotton variety and defoliation treatments individually, and the interaction between these two factors.  In variety trials, cotton plant characteristics thought to contribute to leaf grade, including leaf and bract hairiness, were collected.  The trial was defoliated with a recommended product to determine the varietal impact.  In defoliation trials, fifteen defoliation treatments were applied to a semi-smooth cotton variety and percent defoliation, desiccation, and greenleaf measurements were collected.  In a third trial, multiple defoliation treatments were applied over multiple cotton varieties with varying leaf hairiness ratings.  Each plot was machined harvested and subsamples were ginned through a small scale gin to replicate commercial ginning conditions.  Cotton lint samples were sent to the Fiber and Bioploymer Research Institute in Lubbock, Texas for classing.  A wide range of crop defoliation and desiccation were obtained from the selected treatments.  However, the 2010 data did not have a strong correlation between the defoliation or desiccation level and cotton leaf grade value.  In 2010, a significant increase of leaf grade values was observed as leaf hairiness increased and is likely a key contributor to the current leaf grade issues.   Research trials in 2010 were repeated in 2011 and additional measurements and trials were initiated to further evaluate the various influences on cotton leaf grade, including bract size, leaf and bract hairiness, canopy density, harvest index, and other variables.  The 2010 and 2011 results will be presented at the 2011 meetings. See more from this Division: C02 Crop Physiology and Metabolism
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