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Cotton Defoliation- When to Spray?

Recently Defoliated Cotton – Credit Thomas County Ag

Cotton bolls are opening up so it is time to start making defoliation decisions. I have seen a few fields that have already been sprayed and a lot of cotton that is ready to spray. When making defoliation decisions there are 3 methods we use together to help us know when it is ready for defoliation. The three defoliation check methods are 60-75 percent open bolls, nodes above cracked bolls are at 4 or less, and the knife test.

  1. The open boll method takes in account the percentage of open bolls across the field. When the cotton bolls are on average 60-75 percent open across the entire field it is a good time to spray. If the field is not consistent we usually recommend to leaning towards the 75 percent mark.
  2. The second check method is the nodes above cracked boll test. If you check several spots in the field and most of the plants have 4 or less nodes above the upper most cracked boll then it passes the test. This a good sign that the field is ready for defoliation.
  3. The last test is the sharp knife test. Take a mature boll and try to cut it with a knife. The boll should be hard to cut if the boll is mature. This can be a safety hazard, so I recommend using a ratcheting pvc pipe cutter. They work excellent for this and you don’t end up cutting your hand open. Once you have cut open a few bolls the fiber inside should string and have a tan/brown coating around the seed inside. This means the bolls are mature.
The boll on the left is mature notice the brown seed coat. Photo credit University of Florida Extension

If the cotton field you are checking can pass all three of the tests then it is ready for defoliation. One of the tried and true defoliant recipes is a three way mix of Folex(tribufos), Prep(ethephon), and Drop(thidiazuron). When applying a defoliant spray it is recommended to use 20-30 gallons of water per acre to get good coverage.

For more information about cotton defoliation or assistance with checking fields contact the Evans County Extension Office at 912-739-1292.