Recent rains in some parts of Ohio may not be enough to stem the damage from high temperatures and drought conditions during corn pollination, according to an Ohio State University Extension specialist.
Pollination is the stage in corn development most sensitive to such stress conditions, said Peter Thomison, an OSU Extension agronomist. Severe drought stress before and during pollination could cause a delay in silk emergence. If the delay lasts long enough, little or no pollen is available for fertilization when the silks finally appear, he said.
"When such delays in silking are lengthy, varying degrees of barrenness will result," Thomison said. "This year it's likely that silk emergence will be delayed in many drought-stressed cornfields unless we get some significant rain very soon."
Thomison, who is also a professor in Ohio State's Department of Horticulture and Crop Science, said the drought may be the major headline of the 2012 corn crop. Already, most of Ohio is experiencing moderate drought, with one section in the northwest area of the state near the Indiana border experiencing severe drought as of July 3, according to the U.S. Drought Monitor.
In fact, temperatures have reached over 100 in many parts of the state, with heat index values reaching upwards of 109 in many areas, meteorologists said.
Corn can shut down pollination when it gets too hot and dry, Thomison said, noting that corn will instead try to shed pollen during the cooler periods of the day "before it gets blistering hot."
"Corn growers are worried about the potential for yield loss and whether there will be enough grain to feed their animals," Thomison said.
Growers are also dealing with the impact of recent storms that hit the region. While many farmers in parts of the state that saw pockets of heavy rainfall cheered the rain, many are also dealing with storm damage as a result of the hurricane-force winds in some cases, he said.
"The storms have been localized, kind of like a shotgun blast in that some areas were getting rain but others weren't," Thomison said. "The violent winds associated with the storms have also caused root lodging in some plants and green snap in others, with breakage below the ears, creating plants that won't produce grain.
"These storms have come with a cost: hail and wind damage. You've got a lot of farmers who are keeping their fingers crossed right now."
Growers who want to check the success or failure of pollination can simply wait until the developing kernels appear as watery blisters, which usually occur some 10 days after fertilization. But for growers who'd rather have a faster determination, an ear shake test can determine results quicker, Thomison said.
Test for pollination failure
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.
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 a drought stressed field it may be an indication of pollination failure.