We often use percentage open bolls or nodes above cracked boll to determine when to defoliate cotton. With either technique, it is a good idea to cut some of the younger bolls to ensure that the crop is mature and ready to defoliate.

These bolls are first position bolls from the same plant. The youngest boll on the left was at the top of the plant and the others were one node below each other down the plant. The bolls on the left are not mature. Defoliation of these bolls would result in reduced yields and reduced micronaire. The bolls labeled 5 and 6 are mature and defoliation would not result in reduced yields. If you youngest bolls in a field were similar to the boll labeled number 4 you would probably not reduce yields by defoliating the field. Notice that the more mature bolls on the have a seed coat that is turning dark and easy to distinguish. The cotyledons in the middle of the seed are firm and well-formed.