Many Ohio corn fields have been subject to excessive rainfall this year. The fields where the Ohio Corn Performance Test (OCPT) were planted are no exception. Extraordinary rainfall accumulation has occurred at nearly all OCPT sites. Rainfall accumulations from May 15 to July 18-19 (and there’s been more since then) range from 14.0 to 19.1 inches at test sites in the southwest/west central/central region.
Reports of short, waist high corn tasseling, as well as uneven development and flowering within fields, are not uncommon in parts of the state where heavy rains contributed to extended periods of saturated soil conditions and ponding. Now there are questions as to whether such uneven development will impact pollination and thereby affect yield.
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 R2 or 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, the ear shake technique.
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 a good article, ("A Fast & Accurate Pregnancy Test for Corn"), addressing this topic, available online at https://www.agry.purdue.edu/ext/corn/news/timeless/EarShake.html. There’s also a great video available online at https://www.youtube.com/watch?v=K7DiwD4N0T0