Stress and corn pollination
OK, I think we have all had enough of the 100-degree temperatures. I know this heat and humidity has been tough on the livestock. Be sure to keep a close watch on all livestock while this heat stays around. Make sure they access to have shade, good ventilation and a sufficient quantity of water.
One option to reduce the temperature can be to spray cool water across the roofs of buildings where animals are housed. I’ve used this several times and it works great on smaller buildings. However if your water is hard, it will leave iron stains.
The dry weather has also taken it’s toll. The scattered showers have helped, but we are in need of much more. The good news is next week looks a little cooler. Temperatures will only be slightly above normal with rainfall below normal. Normals are highs in the 80s and lows in the 60s with about an inch of rain typically. However, The National Weather Service is not projecting a break in the above normal temperatures and below normal rainfall pattern through July.
The first half of 2012, has been almost the exact opposite of 2011. In 2011 Rainfall was 5–10 inches above normal in most places with a few higher totals. In 2012 rainfall is generally 3–10 inches below normal. I guess if you average two extreme years and you get normal.
We are not the only ones affected here in Ohio by abnormally dry to severe drought conditions. Peter Thomison, OSU Extension Specialist, said 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 hardly any rain since early June. 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.
Thomison says that 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.
Thomison says 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 one and a half 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 one to three 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”, Thomison said. “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” 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, recently wrote a good article, “A Fast & Accurate Pregnancy Test for Corn,” addressing this topic, available at tinyurl.com/7o4adbp. There’s also a great video available at tinyurl.com/7a969z3.
The Woods in Your Back Yard: From 9 a.m. to 3 p.m. July 20 at Deer Haven Preserve in Delaware County, OSU Extension is offering a workshop where landowners can come and learn which trees and shrubs are “good,” and what they are good for. You will also learn how to attract wildlife, improve the health of the trees, deal with invasive species and more. Cost is $35 per person and includes lunch and handouts. Register at woodlandstewards.osu.edu, email email@example.com or call 614–688-3421.
Rob Leeds is an OSU Extension educator.