Jeff Burbrink

By JEFF BURBRINK
Extension Educator, Purdue Extension Elkhart County

GOSHEN — For the past two weeks, I have written about the tassel and silks on a corn plant. This week, the focus of my article will be the ear.

An “ear” seems like a funny name for a plant part. It is derived from an ancient word, “ahs,” which meant, “husk of corn.” Ears first begin to develop when the corn reaches the V5 stage, or five visible leaves showing on the stalk. With a hand lens, you might be able to find as many as 12 tiny ears beginning to form on a V6 plant. With modern genetics, the plants are bred to abort the extra ears in favor of having one, possibly two larger ears.

By V6, the number of rows of kernels around the ear is determined, a process that is largely genetic, but can be influenced by stress such as drought or flooding. The number of rows on an ear are always an even number. The husk, which are modified leaves that protect the kernels and silks, begins to form at this time also.

Between V12 and tasseling, the number of potential kernels per row is determined. Genetics, once again, plays a role in this, but it can be affected by stress as well.

Silks begin to elongate under the husk as the tassel emerges. Since each silk is attached to just one kernel, and silk is the structure used to transit the male genetic material to the kernel, the ear filling process can be greatly affected by drought, heat, insects and other stress on the plant at this stage.

The fertilized kernels begin to form white, liquid-filled “blisters” on the cob about 10 days after silking. The silks, meanwhile, detach from the kernels and turn brown. Starch begins to accumulate in the future seed and the first tiny root and leaf form in the embryo. The moisture content of the seed is about 85 percent at this point.

About 20 days after silking, the kernels are turning yellow and a milky, white fluid can be found inside the kernel. This is the same stage that sweet corn enthusiasts like to call the roasting ear stage. The moisture content is still about 80 percent and heat or moisture stress can still have an effect on overall yield.

The dough stage occurs about 25 to 28 days after silking. The milky fluid begins to solidify as more starch accumulates in the kernel. The cob is now turning from light green to a pink or red, the kernels have reached 50 percent of their mature weight, while the moisture content has dropped to below 70 percent.

Ten days later, the kernel begins to dent. Five very small leaves and some small roots have developed inside the embryo. A very distinct line develops near the dent end of the kernel and progresses to the tip of the ear over the next three weeks. The “milk line” marks the boundary between the milky and starchy portions of the developing seed. Stress during the dent stage can still limit yields. Estimated yield loss if the entire plant dies at full dent is about 40 percent, while at half milk line the loss is about 12 percent.

Physiological maturity is reached at 55 to 65 days after silking.  At this stage, the milk line has disappeared and the kernel is safe from frost injury. A black layer forms between the tip of the kernel and the cob, severing their relationship forever. The moisture content is generally in the 30 percent range. Grain yield is pretty much locked in unless the stalk or ear are compromised physically by disease, stalk-boring insects or wind.

The final phase of development is harvest maturity. While technically the corn can be harvested at physiological maturity, most people wait until the grain has dried well below 25 percent moisture content to begin harvest. This allows the corn to dry in the field, toward the target moisture content of 14 to 15 percent, where grain can be stored in bins long term. The longer the grain dries in the field, the less expense the grower has in drying costs. However, as winter approaches, the risk of stalk or ear compromise increases.