I know many are wondering when they can start backing off and even shutting down irrigation water over the next few weeks. Again, the nodes above white flower (NAWF) measurement can be extremely helpful. This will let you know where your current top boll position is and how old previously set bolls are.
As an example, if we have a white bloom three nodes down from the top, I will say you have 2 NAWF. I am only referring to first position fruit.
So just below this white flower should be a small boll which would be approximately 1-3 days old. The boll directly below it was formed 60 heat units before this small boll. Which on average is 3 days this year. So, if there are 5 first position bolls present below this top small boll, we can estimate that the oldest boll is somewhere around 15-18 days old right now.
In other words, that oldest boll would have been a bloom around July 19. Now that you know how to judge the age of a boll you should consider which of the uppermost bolls you can realistically take to harvest.
Let us again be realistic and say that the bloom a week from now on August 13 is the last one we think we have time to mature out. This flower will then be a boll on August 14. This boll cannot be water stressed for about 20 days. So, this plant needs good available water through September 3. This moisture may come from irrigation or rain.
After September 3, this boll can take moderate stress, meaning that the plant can wilt on a hot afternoon if it completely recovers by the next morning. Then when this last boll is 45 days old or in this example September 28, it can take severe water stress and it should not cause quality or yield loss.
In fact, to continue to water any later could delay maturity, and cause harvest problems.
So, I throw these dates out only as an example. You will have to look at your fields, take into consideration your capacity to irrigate, and what is a realistic target for last boll to be set. I will be glad to help assess a field situation with you.