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PGR Decision Guide (Use only as a guide)

The total number of nodes present on a cotton plant can be used to assess plant vigor or to provide an indication of stage of development. To get an accurate count of total nodes, it is necessary to start at the first true leaf node above the cotyledons (node 1) and count upward until reaching the uppermost unfurled leaf. A common pitfall in counting total nodes is that one may miss lower leaf nodes that shed as the canopy gets larger. It is especially important to be hands on in this situation because the only way to get a true count of total nodes in a dense canopy is to feel the scars on the mainstem where the earliest true leaves used to be. For PGR management, it is not always necessary to count all nodes since the region of active stem elongation is near the top of the plant. Growth management using PGRs is a topic to which an entire newsletter could be devoted, but this is not our purpose here. What is important is that it is often necessary to know the length of the fourth internode. The fourth internode would be the length of stem between the fourth and fifth node. Obviously, cotton variety, environmental conditions, PGR timing, and application rate are important considerations, but as a general rule, a fourth internode length greater than 2 to 3 inches indicates a need for PGR application. A simplified version of this for those of us who don’t carry rulers around with us all the time is to determine if three or more fingers can fit in the fourth internode (Figure 3). If not, PGRs are likely not needed.
Figure 3