Defoliating cotton is an art. Each year presents different challenges. Once the field reaches 75% open bolls or 4 or less nodes above the upper cracked boll it is time to pull the trigger.
Cotton Defoliants each have a different job. Most farmers have a general “recipe” that they use for defoliation. If you have questions about your specific situation please give your county agent a call. I wanted to post a few charts that may help you when making defoliation decisions.