Here is a handout and a few charts regarding cotton defoliation from UGA Cotton Agronomists, Jared Whitaker and Mark Freeman:
Cotton Defoliation Guide (Front)
Cotton Defoliation Guide (Back)
With the talk of there being a shortage of thidiazuron (Dropp), a good alternative will be thidiazuron+diuron (Ginstar, Adios, Cutout).
