I walked several fields last week that looked like mid-August cotton. Blooms were nearing the top of the plant, the result of a couple of weeks of high temperatures, and, in some cases, scarce rainfall. Vegetative growth was good; boll retention was good; but the plant was running out of positions for new fruit.
An accepted technical definition of “cut out” occurs as flowers near the upper part of the canopy, when the crop reaches 5 nodes above white flower (NAWF) – that is, when there are only 5 nodes of main stem growth above a 1st position white flower.
It indicates or at least suggests that effective boll set is racing towards a finish. In good growing conditions, cotton can maintain 5 NAWF for an extended time, which means that the 5 NAWF designation does not always signal “the end is near.”
In stands with lower plant populations, vegetative branches and 2nd and 3rd position bolls may also add to the final tally of harvestable fruit. Moderate temperatures, good soil moisture, and adequate fertility are the logical means to prolonging effective boll set.
As fields reach mid-bloom and as flowers appear in the upper canopy, expect significant fruit shed. The plant simply cannot sustain all the possible squares and bolls. Young bolls are the first to shed (see the related image). Squares are next.
However, if a boll remains intact for 10 days or more, the vascular connection becomes such that it rarely aborts.