Late Corn Crop Under Stress

Late Corn Crop Under Stress

Late-planted Ohio corn may show signs of heat stress and reduced yield potential as extremely hot, dry days plagued the state recently, according to an Ohio State Extension corn scientist.

When corn is planted in wet soils, root systems often don't develop as well as they would have in drier conditions. And in years with a significant number of abnormally hot, dry days, wet conditions at planting can be very troubling for farmers and yield potential.

Peter Thomison, a professor in OSU's Department of Horticulture & Crop Science, says lack of rain may be the major headline of the 2011 corn crop.

"There are parts of the state, areas in Brown County for example, that got 8 inches recently, while other areas in the same county didn't get a drop," Thomison says. "In a lot of the northwestern counties that needed rain, some areas got an inch and others didn't get any."

Because of the challenges in getting the crop in the ground, Thomison says Ohio essentially has two crops: one planted early and one late. While some corn was planted in April, he estimates as much as 30-40% of corn was planted in a window from May 10-12, while the majority of the state's crop was planted after Memorial Day.

Those crops are naturally very different, Thomison notes. The corn planted in mid-May, he said, is at or near tasseling now, while corn planted after Memorial day is anywhere from stages V10 to V14. Some corn planted later in June may only be at the V6 stage.

"Given the variability of corn in the fields, some of the later corn isn't rooting very well because of soil conditions at planting - things like sidewall compaction and varying planting depths," Thomison says. "Because of the intense heat and lack of rainfall this summer, some of that corn isn't performing well, even though it was planted in a moist soil bed. Some of this corn could be six feet tall, and in the same field there's corn waist high."

Along with the root structure and development issues, heat may affect yield potential by limiting the number of kernels developed. Thomison and his Extension colleagues have heard reports from some areas of the state about corn rolling relatively early each day and exhibiting moisture-related stress throughout the day.

While conventional wisdom says heat stress at pollination is a problem, Thomison says if hot and dry conditions persist, the real problem this year will be kernel abortion instead of limited pollination.

"If we're looking at temperatures above 90 degrees sustained over a week, combined with soil moisture deficits, the impact on corn could be devastating," he says. "These high temperatures alone may not jeopardize pollination, but in conjunction with water stress they can result in significant kernel abortion after pollination, during early grain fill. So, the ovules may get pollinated, but if we have inadequate moisture, the kernels will just abort and we'll see tip dieback."

He recalls similar challenges in 2002, another year characterized by late plantings, where lack of moisture produced "nubbin ears" that significantly lowered yields. He sees potential yield loss of up to 5-10% per day if fields experience severe moisture stress in the two weeks before tasselling.

Recent windstorms throughout the Eastern Cornbelt also caused problems because of the issues with root development. But Thomison says corn stalks for the most part have already bounced back. In most cases the wind damage was limited and localized, but some problems may still exist with corn stalk crimping, or pockets of green snap.

With expected rainfall totals at or below normal for the remainder of July and August, Thomison said he remains concerned about how well Mother Nature will treat Ohio farmers through season's end.

"The long-term forecast, to be brutally honest, is not promising," he says. "Some people will talk about maturity this year, but I'm more afraid the crop may just die of moisture stress in August."

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