Field corn is an important food crop for both humans and livestock. It also provides raw material for many products including corn oil, fuel alcohol, starches and sweeteners. Field corn grows in stages with critical developmental milestones occurring on the way to maturity at about 18 weeks. Corn growth stages are indicated by the number of leaf collars on the stalk where leaf blades break away from the stalk, and by ear development after fertilization.
Planting to Emergence
The first stage of corn plant development starts when corn seed is planted. The seed absorbs soil moisture, awakening the corn plant embryo in the seed. The embryo feeds from the seed to shoot out roots and a stalk. In one to two weeks after planting, the corn shoot emerges from the ground and unfurls its first leaf.
After emergence, the corn plant starts vegetative growth, adding a new leaf collar about every three to five days. Roughly three weeks after emergence, the corn plant has reached the growth milestone designated vegetative growth stage 6, or V6, for short. At this stage, the growing point has moved above ground and the plant is roughly knee high. The plant has developed the very tiny side buds that will develop into the ears and the top bud that will become the tassel. Over weeks four through eight, the corn plant completes its vegetative growth, reaching about 7 feet tall, and sets the number of ovules on each ear that will develop into kernels.
Tasseling and Silking
In week nine after emergence, the typical corn plant sprouts its tassel, the male flower that pollinates the ears. This stage is known as VT. At around the same time, the ears produce sticky corn silk, which is the female flower that the pollen will fertilize. Each strand of silk connects to an ovule on the ear. A typical ear of corn will have about 750 ovules that will become about 500 mature kernels. The tassel sheds about 500,000 pollen grains per day into the air. Pollen shedding lasts for about a week. At this point, corn enters the reproductive phase at stage R1 where the pollen fertilizes the silk.
In week 10 after emergence, the corn ears enter the R2 stage where the fertilized ovules resemble little white fluid-filled blisters. In weeks 11 to 13, the blisters have become pale yellow kernels. The fluid in them becomes milky and starts to turn starchy. In weeks 14 and 15, the kernels reach the R5 stage. They are bright yellow, their interior is dough-like and the top shows a shallow dent. In weeks 16 to 18 after emergence, the corn ears complete their kernel development to the R6 stage where the ears are at full physiological maturity. At this point the corn plant’s leaves turn brown and dry out.
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