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Alphabet soup of corn development

John Brien
John Brien

When discussing growth and development of a corn plant, a grower very quickly is submerged into a world of alphabet soup. There are all kinds of Vs, Rs and Ts used and while the system was designed to make things easier, all the letters grouped together can be quite confusing.

Prior to silking, corn growth is measured in “V” stages or vegetative stages. For each new collar (fully developed leaf) a corn plant moves to another “V” stage. For instance a corn plant with five collars is considered to be at V5 growth stage. After VT (tassel emergence) the development of the corn crop is marked in “R” stages or reproductive stages.

There is considerable amount of effort and time spent on the vegetative stages, but little time spent on the rest. Below is a quick guide to help follow the corn crop from tasseling to harvest:


R1 — silking

This occurs when silks have emerged from the tip of the ear shoot on 50% of the plants. R1 is the stage most growers focus on due to its importance on the final yield. Typically silks are receptive to pollen for 10 days. Pollen from the tassel falls unto the silks, then “grows” down the silk to fertilize the ovule (kernel). The exciting part of pollination is that the corn plant over produces pollen to make sure fertilization occurs. Each corn plant has the potential to produce 5 million grains of pollen or 5,000 grains of pollen for each silk. Therefore unless the corn plant is under extreme stress, it is able to pollinate all the potential kernels quite easily.


R2 — blister stage

This occurs 10 to 14 days after silking. The silks are mostly brown and drying rapidly. Upon pulling the husk back, the kernel is visible and looks like a blister on the cob. The kernel is filling with clear fluid and the radicle root, coleoptile and first embryonic leaf have formed in the embryo. Any stress during blister stage will cause kernels from the tip to abort.


R3 — milk stage (Roasting Ear Stage)

This takes place 18 to 22 days after silking. The color of the kernel changes from a white/clear to an orange/yellow color. Once the kernel turns to the orange/yellow, the chance for kernel abortion greatly decreases. The goal when looking at ears at the milk stage is to have the entire ear change colors at the same relative time. The longer the process to change colors on the top portion of the ear the more chance those kernels could be aborted.

There is rapid accumulation of starch in the kernel during the milk stage. Also the endosperm development is complete and the growth of the kernel is attributed to cell expansion and starch fill-in.


R4 — dough stage

This occurs 24 to 28 days after silking. Dough stage is simply that, the contents of the kernel have begun to change into a dough or paste-like substance. By R4 the kernels have accumulated about half of their final dry weight. The cob is now gaining color and is likely a light red or pink. By this stage, four embryonic leaves have developed in the embryo. Kernel abortion at this stage is highly unlikely.


R5 — dent stage

This occurs 35 to 42 days after silking. Kernels are dented at the top of the kernel and have begun to dry down. During dent stage a grower can follow the “milk line” that separates the yellow from the white on the kernel. The milk line will progress down as the kernel matures and the starch hardens. Stress at this time will only reduce kernel weights, not kernel numbers.


R6 — physiological maturity (black layer)

This occurs 55 to 65 days after silking. At R6 all kernels have reached their maximum dry matter accumulation and a black layer will be visible at the base of each kernel. Kernel moisture in now between 30% to 35% and will begin to lower depending on the hybrid, plant health and environmental conditions.

The formation of grain is an amazing part of a corn plant’s responsibility. Even though there is very little most growers can do to impact yield after pollination, knowing what is happening can make walking those corn fields in July and August much more enjoyable!


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