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Check cornfields for pollination success

Corn Illustrated: See what you can learn in the field at pollination time.

Dave Nanda

May 23, 2023

3 Min Read
Dave Nanda holding ear of corn with long silks hanging down
SHAKE AND LOOK: Dave Nanda demonstrates the shake test on this ear of corn. Silks that remain attached to the ear connect to ovules not yet fertilized. Tom J. Bechman

The time of year to scout cornfields and check for the payoff is approaching. How well did ears pollinate? What are the yield prospects?

The best way to assess pollination success is to pull a few ears at random and evaluate kernel set. Pull those husks back and see what ears look like. If pollination is still happening, you may find some silks still attached to the ear.

Every silk is attached to one ovule on the ear that could form a kernel, if properly pollinated. If you look at the silks with a magnifying glass, you will see fine hair on every silk. This fine hair traps pollen grains. The job of each silk is to catch and deliver genetic material in the pollen to the ovule. Most pollen grains fall on silks by gravity or wind. If proper weather conditions exist, a kernel will form.

If proper pollination occurs, each ovule that is fertilized produces one kernel on the ear. So, 480 kernels on an ear mean 16 rows, each with 30 successful fertilizations, must occur. This would be a short ear today. If there are 18 rows and 38 kernels per row, that would be 684 kernels on a longer, girthy ear.

After genetic material in the pollen grain reaches the ovule and fertilization takes place, the silk falls off the ear. Its job is done. If an individual silk does not get pollinated and the ovule is not fertilized, the silk remains attached, hoping to get fertilized. Fertilization starts at the butt of the ear and progresses toward the tip. Kernels at the tip are pollinated last.

If stress develops, tip kernels are the first kernels the plant aborts. If the plant decides it can’t fill all kernels that were fertilized, it aborts kernels, starting at the tip, until it believes it can fill all remaining kernels.

The shake test

The classic test to determine how far pollination is progressing is the shake test. It was made famous by Bob Nielsen, a retired Purdue Extension agronomist. It is simple to do and provides insight into the pollination process.

Once you have pulled shucks back on an ear, hold the ear out horizontally in front of you and shake it. If silks fall off, those ovules pollinated, and kernels should develop on the cob. If silks remain attached to the ear, those silks are connected to ovules that did not get pollinated. If there is still pollen in the field, there is a chance they can still be pollinated. If there is no pollen remaining, then those ovules will be aborted.

Weather can affect whether all silks pollinate as they should. Under extreme heat or drought stress, pollination will be disrupted. Insects can also interfere with pollination success. Silk clipping, usually by Japanese beetles or adult rootworm beetles, can interfere with pollination if beetle numbers are high enough and they constantly clip silks within one-half inch of the ear. Insecticides may be necessary if these bugs are high in numbers. That’s one more reason why it’s important to walk fields at pollination time.

Nanda is director of genetics for Seed Genetics Direct, Jeffersonville, Ohio. Email [email protected] or call 317-910-9876. Please leave a message.

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About the Author(s)

Dave Nanda

Dave Nanda is director of genetics for Seed Genetics Direct, Jeffersonville, Ohio. Email [email protected] or call 317-910-9876. Please leave a message.

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