When to apply defoliants has been a problem for cotton producers for more years than I have been farming. The first practical defoliant material was calcium cyanamid, and it appeared on the scene several years before there were mechanical harvesters. Cyanamid was used then in the mistaken notion that removing cotton leaves would hasten boll opening and also to facilitate hand harvesting.

When mechanical cotton pickers first appeared, cotton gins didn't have seedcotton cleaning equipment and defoliants were an economic necessity. Attention was focused early on the boll period. The fact that later set bolls required many more days to mature than earlier ones was widely reported. Today it is more precise to report the boll period in heat units or DD-60's.