A heat wave for up to two weeks beginning Friday could mean less corn to harvest, contrary to the adage Iowans have passed along for generations.
Corn doesn't like it hot, especially during mating.
Corn plants are putting out male tassels and female silks this week. Next week, pollination will create the kernels that are the heart of the corn crop, which could bring in a record $17 billion to Iowa this year.
Agronomists and meteorologists agree that 86 degrees is the best condition for corn reproduction. Instead, the tassels and kernels will get temperatures averaging 95 degrees or more.
"The timing of this heat wave couldn't be worse," Des Moines meteorologist Harvey Freese said. "The old saying about hot weather being good for corn isn't true during pollination."
Pollination problems cause smaller ears with fewer kernels, which shows up as smaller yields at harvest. That could be the hiccup that many have feared since before planting began in April.
The amount of U.S. corn is expected to shrink to 15-year lows by late summer, reduced by a smaller crop last year and record demand from ethanol plants and other countries. A smaller-than-expected crop could cut profits for ethanol producers, livestock producers and other users of corn.
It could also have an impact in the grocery store: Corn prices have doubled since mid-summer 2010, fueling increases in meat prices as much as 10 percent for hamburger and 25 percent for bacon.
The Agriculture Department said the supply situation won't ease much through next year, even though farmers have planted up to 5 percent more corn acres this year than last.
Arlan Suderman of Farm Futures Magazine said traders expect the heat to reduce corn yields across Kansas, eastern Iowa and central Illinois, and "cause at least some stress in southern Iowa, Missouri and southern Nebraska, as well."
"That's not what you want to see," State Climatologist Harry Hillaker said.
Agronomist Bob Streit of Boone said hot weather puts the male and female parts of the corn plant into what he called "temporal incompatibility."
"It's like, the guy shows up for the date at 8 p.m. and the girl was expecting him at 9," Streit said. "After that, things might not happen quite the way the fellow hoped for."
The heat wave follows heavy winds early Monday that knocked down corn from central Iowa as far east as Michigan and floodwaters along the Missouri River that are expected to drown about a half-million acres of corn.
"You throw a heat wave at this year's corn crop and who knows where the price might go," said commodity trader Sue Martin of Ag & Investment Services in Webster City.
On the Chicago Board of Trade on Wednesday, the July corn contract rose 30 cents per bushel to $7.27. The December contract, which prices the corn in the field now, rose 22 cents per bushel to $6.80.
Iowa's last great heat-drought combination, in 1988, pared 30 percent from corn yields.
A similar drop in yield from Iowa's 2009 record of 182 bushels per acre would push the 2011 yield down to 128 bushels per acre, which would be the lowest yield since 1995.
Iowa State University agronomist Roger Elmore said 1988 was before genetically altered biotech corn came into wide use.
"Every evidence is that biotech corn takes stress better than the traditional hybrid corn," Elmore said.
But Elmore also noted that the greater concentration of corn plants - from about 24,000 to 26,000 plants per acre in the 1980s and '90s to 32,000 to 34,000 plants today - means that soil moisture will be sucked up faster.
"A cornfield takes one-third of an inch of water per day during pollination," Elmore said. "Iowa is in pretty good shape this summer for soil moisture, with four inches or so in the ground. We could go a week with very hot weather without rain and probably be all right, but it will become dry very quickly."
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