As young corn plants grow, several of the lower leaves on the plant can be destroyed. This can make it difficult to accurately stage the plant once it grows beyond the V6 to V8 growth stages. The main growth-staging method is the leaf collar method. It begins with the first rounded leaf that emerges from the plant.

 Use the uppermost, fully visible leaf collar

On plants where all leaves are attached, count all leaves with a collar - including the cotyledonary l.

Locate where the sheath of the final leaf is attached to the stalk — that is the node for that leaf.

From that node, count down through the nodes to the pithy triangle at the bottom of the crown. The pithy triangle typically includes the first four nodes of the plant. The node above the first elongated internode is the V5 node.

In a seed, the embryo already contains the first 4 to 5 leaves of the plant. Once germination begins and growth initiates, rapid development of additional leaves, the ears, and the tassel soon follow. All the leaves are initiated by the time the plant reaches the V5 to V6 growth stages; modern hybrids develop 16 to 22 total leaves. After the leaves have been initiated, the tassel forms at the apical meristem. Secondary meristems, the future ear(s), will develop at stalk nodes.

Over the course of the early growing season, the speed of leaf development changes. From about V1 to V10, it takes approximately 85 GDUs per leaf to emerge. This averages about 5 to 6 days per leaf in early May to 3 to 4 days per leaf in June. From V10 until the end of vegetative growth, leaf development accelerates to about 50 GDUs per leaf or one leaf every 2 to 3 days.

At V7, the tassel of the plant can be found by carefully dissecting the plant. As the tassel develops, it is pushed upward as it rides at the top of the elongating stalk. Corn plants are very prolific, with an earbud associated with every leaf on the plant. If you carefully dissect a V10 plant, you can easily find 8 to 10 ear shoots behind the leaf sheaths along the stalks. Typically, the harvested ear from a plant will occur between the 12 and 14 leaf. If the uppermost harvestable ear is damaged prior to pollination, the next lower ear will become the active ear.

Ear size determination is an ongoing process that begins near V6 and ends roughly one week before pollination. The kernel row number (always an even number) is set just after the V6 stage of development. Additional ovules initiate as the ear develops until about one to two weeks before pollination. Rows around are primarily genetically controlled, and kernels per row are environmentally controlled. 

Ovules are added first at the base of the ear working outward to the ear tip. At the end of ear development, the number of potential kernels has been set — usually between 700 to 1,000 kernels/ear. Stress, or damage to the plant from that point on can cause significant reductions in kernel count. Typical harvestable ears average between 400 to 600 kernels/ear.


: Corn Growth and Development. https://www.agry.purdue.edu/ext/pubs/AGRY-97-07_v1-1.pdf
