CORN Newsletter: 2008-25, August 4, 2008

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C.O.R.N Newsletter 2008-25
August 4, 2008 - August 10, 2008

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Assessing the Success of Pollination in Corn
by Peter Thomison


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Many corn growers want to know what impact recent dry weather has had on corn pollination, the stage in corn development most sensitive to such stress conditions. When severe drought stress occurs before and during pollination, a delay in silk emergence can occur. Sometimes the length of this delay is such that little or no pollen is available for fertilization when the silks finally appear. Although it’s rare, when such delays in silking are lengthy, varying degrees of barrenness will result.

Others may want to determine the impact of silk clipping by corn rootworm beetles and Japanese beetles on pollination. According to corn entomologists, damage by silk clipping insects is usually limited unless the silks are being continuously clipped back to less than 1/2 inch long before pollination is 50 percent complete

There are two techniques commonly used to assess the success or failure of pollination. One involves simply waiting until the developing ovules (kernels) appear as watery blisters (the "blister" stage of kernel development). This usually occurs about 1 1/2 weeks after fertilization of the ovules. However, there is a more rapid means to determine pollination success.

Each potential kernel on the ear has a silk attached to it. Once a pollen grain "lands" on an individual silk, it quickly germinates and produces a pollen tube that grows the length of the silk to fertilize the ovule in 12 to 28 hours. Within 1 to 3 days after a silk is pollinated and fertilization of the ovule is successful, the silk will detach from the developing kernel. Unfertilized ovules will still have attached silks.

Silks turn brown and dry up after the fertilization process occurs. By carefully unwrapping the husk leaves from an ear and then gently shaking the ear, the silks from the fertilized ovules will readily drop off. Keep in mind that silks can remain receptive to pollen up to 10 days after emergence. The proportion of fertilized ovules (future kernels) on an ear can be deduced by the proportion of silks dropping off the ear. Sampling several ears at random throughout a field will provide an indication of the progress of pollination.

Unusually long silks that are still "fresh" period are a symptom that pollination has not been successful. Unpollinated silks continue to elongate for about 10 days after they emerge from the ear husks before they finally deteriorate rapidly. During this period, silks become less receptive to pollen germination as they age and the rate of kernel set success decreases. If you observe unusually long silks in drought stressed field it may be an indication of pollination failure.

Dr. Bob Nielsen, the corn extension specialist at Purdue University, has written a good article, ("A Fast & Accurate Pregnancy Test for Corn"), which includes excellent pictures showing this problem; it’s available online at
http://www.agry.purdue.edu/ext/corn/news/timeless/EarShake.html (verified 8-4-08)

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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