Peter Thomison, OSU corn specialist, recently assessed the potential for pollination in Ohio's corn crop. Here are some of the comments he made in the article which ran in the C.O.R.N. newsletter.
"Reports of short, waist high corn tasselling, as well as uneven flowering within fields, are not uncommon in parts of the state which have received negligible rain since early June," Thomison says. "Many corn growers want to know what impact drought stress 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. When such delays in silking are lengthy, varying degrees of barrenness will result. This year it's likely that silk emergence will be delayed in many drought-stressed corn fields unless we get some significant rain very soon."
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, according to Thomison.
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, he says. 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, Thomison says. 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.
Bob Nielsen, the corn extension specialist at Purdue University, recently wrote a good article, ("A Fast & Accurate Pregnancy Test for Corn"), addressing this topic, available online at http://www.kingcorn.org/news/timeless/EarShake.html. There's also a great video available online at http://www.youtube.com/watch?v=K7DiwD4N0T0&feature=player_embedded