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OSU Extension

College of Food, Agricultural, and Environmental Sciences

CFAES
July 25, 2017 - 8:00am -- Anonymous

Although a few cornfields have already completed the pollination process, many fields are at that development stage or soon will be.  With that in mind, Peter Thomison, OSU Extension corn specialist provides the following explanation of the corn pollination process.

The pollination period, the flowering stage in corn, is the most critical period in the development of a corn plant from the standpoint of grain yield determination. The following are some key steps in the corn pollination process.

Most corn hybrids tassel and silk about the same time although some variability exists among hybrids and environments. On a typical midsummer day, peak pollen shed occurs in the morning between 9:00 and 11:00 a.m. followed by a second round of pollen shed late in the afternoon. Pollen shed begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen. Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid- morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. However, most of it settles within 20 to 50 feet.

Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Little to no pollen is shed when the tassel is wet so there is little chance of pollen washing off the silks during a rainstorm. Also, silks are covered with fine, sticky hairs, which serve to catch and anchor pollen grains.

Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours. A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days.  This usually provides adequate time to pollinate all silks before pollen shed ceases.

Pollen of a given plant rarely fertilizes all the silks of the same plant. Under field conditions, 97% or more of the kernels produced by each plant are pollinated by other plants in the field. Each tassel contains as many as 2 million or more pollen grains, which translates to at least 2,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are a problem under conditions of extreme heat and drought; they may also occur in fields characterized by uneven emergence in later emerging plants.  Poor kernel set is more often associated with poor timing of pollen shed and silk emergence – with silks emerging after pollen shed. However, modern hybrids rarely exhibit this problem unless they experience extreme drought stress.