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Corn pollination and growing degree days

Some corn producers have started seeing some tassels in their cornfields during the last week. The question still remains: will we have enough Growing Degree Days (GDDs) to get that crop to maturity this summer and fall?

This year's corn pollination period is going to vary widely across the state and from field to field. The late-planted corn may not be tasselling until early August.

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. Stress conditions such as drought or hail damage have the greatest impact on yield potential during the reproductive stage. The following are some key steps in the corn pollination process.

Pollen shed usually begins two to three days prior to silk emergence and continues for five to eight days with peak shed on the third day. On a typical midsummer day, peak pollen shed occurs in the morning between 9 and 11 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.

Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet. 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 and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.

Pollen of a given plant rarely fertilizes all the silks of the same plant. Under field conditions, other plants in the field may pollinate 97 percent or more of the kernels produced by each plant. The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains, which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot.

Shortages of pollen are usually only a problem under conditions of extreme heat and drought.

Ideal growing conditions of adequate water and nutrients are critical factors during pollination, and will have a great impact on corn crop yields. With the cool spring in 2008 and late planting of corn, tasselling/silking has been delayed. So with corn maturity based on heat units or GDDs, we will need some warm days and nights this fall to get that corn crop in the bin.

A general rule of thumb as far as days to maturity is found in the table above.

For more information on corn maturity, pollination, Growing Degree Days (GDDs), and the upcoming Corn Field day in Ogema contact me: Will Yliniemi, Hubbard/Becker County Extension Educator at 1-218-732-3391, 1-218-846-7328 or by cell at 1-218-252-1042, or by e-mail at

Corn Field Day Aug. 1 in Ogema

Area producers are invited to attend a Corn Field Day on Friday, Aug. 1, at Bill and Eric Zurn's corn production field located two miles south of Ogema on Highwy 59 and two miles west on County Road 155. The Field Day will begin at 9:30 a.m. and conclude at noon.

The agenda for the day includes: Corn Production Tips by Jeff Coulter, U of M Extension Corn Specialist; Corn N, P & K Starter and Hybrid fertility plots and Corn Jumpstart Inoculants X Avail Trial by Dan Kaiser, U of M Extension Nutrient Management Specialist; Corn Nitrogen Rate Study by Russ Severson, U of M Extension Crops Educator; Corn Sulfur Study by Ray Bisek, U of M Extension Educator (Mahnomen/Polk/Norman); and Corn Insect Update and Outlook by Phillip Glogoza, U of M Extension Crops Educator.

For more information about the Ogema Corn Field Day please contact: Will Yliniemi, Becker County Extension at 1-218-846-7328 or cell 1-218-252-1042; or Ray Bisek, Norman County Extension at 218-784-7183.