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* Corn yields threatened in top crop state of Iowa
* U.S. drought conditions intensified this week
* Highs 100-105 F common across US crop belt on Friday
By Christine Stebbins
CHICAGO, July 6 (Reuters) - Fears are rising that grain crops in the core of the U.S. Corn Belt - the top corn-producing region in the world - will suffer big losses that are already causing farmers to plow up fields in other regions of the belt, agronomists and traders said on F rid ay.
Iowa and Illinois - which produce about a third of all U.S. corn and soybeans -- are threatened by the harshest heat wave in more than half a century. Blistering temperatures, combined with little rain, are stressing corn during pollination, the key growth stage.
“By Sunday or Monday if we don’t get rain here we will be losing anywhere between 7 to 9 percent of our yield potential,” said Roger Elmore, corn agronomist at Iowa State University in Ames, Iowa. “If it drags on into next week, it is going to be worse.”
Drought conditions, which intensified during the past week across the central United States, have caused irrevocable damage to crops in Missouri, Indiana and even southern Illinois, where farmers are cutting stunted corn for silage, a low-grade feed for cattle.
“Next week is critical for Iowa,” said Elmore. “Even the crops on good soils are going to start showing a lot of stress going into next week if we don’t have rains soon.”
Mike Hutjens, University of Illinois professor of animal sciences, said corn plants, especially in the southern third of the state, are showing irremediable stress from the heat and drought.
“Corn plants are firing from the roots up the stalk of the corn plant,” he said, meaning stalks are drying out. “Some corn has tasseled, which may not pollinate, resulting in barren corn stalks” with no ears of corn.
Agronomists said calls by farmers for crop insurance claims continued to rise this week, and the worst is far from over for both farmers and consumers, as well as corn processors and exporters worried about supplies and soaring grain prices.
The region’s soybean crop is also stressed, but was planted a month behind corn. Its key growth stage comes in August.
“Livestock producers may be able to purchase drought-stress corn locally, as it has little value for grain or hog producers,” Hutjens said. “Like livestock producers in the southwest areas of the United States last summer, dairy managers are asking what will be available and affordable for their dairy cattle this fall and winter? Drought-stress corn silage may be an alternative locally. Consumers will share in the cost of drought-stressed corn this summer as corn yields may be quite low, raising food prices and ethanol costs.”
Indiana and Missouri have seen the brunt of corn losses so far, as those states are among the hardest hit by the drought. Indiana ranked fifth in 2011 corn production, with about 6.8 percent of the crop, while Missouri ranked 10th in corn production.
“There are very few parts of the state where corn is not under severe stress,” said William Wiebold, an agronomist for the University of Missouri.
Highs of 100 to 105 degrees Fahrenheit were common from Kansas to Indiana on Friday. The heat wave was expected to break by Sunday, with highs in the 80s F most of next week, forecasters said.
But the outlook for rain remains limited.
Joel Widenor, an agricultural meteorologist with Commodity Weather Group, expects most of the Corn Belt to stay dry this weekend. The best chance of rain is forecast for Minnesota, North Dakota, northeastern Iowa and southern Wisconsin, which could see a quarter-inch to an inch of rainfall over the weekend.
“By early next week there is a some chance of scattered showers for central and southern Missouri through the southern parts of Illinois, Indiana and Ohio. But nothing overly organized, just some scattered rains to give crops a little relief,” Widenor said.
The National Weather Service outlook for July 11-15 calls for above-normal temperatures and below-normal rainfall for the crop region stretching from Nebraska to Ohio. Normal temperatures and below-normal rains are forecast for Missouri.
Iowa State’s Elmore said he ran crop simulation models over the last 24 hours that showed as of July 2 that corn yields on good Iowa soils with some moisture have not been hurt. But that is changing drastically with each day Iowa goes without rain, he said.
“Iowa corn needs 3/10 to 4/10 inch or rain a day. This is the peak water use for the whole season. If the plant can’t get water soon it starts shutting down. It’s already happening in some places in Iowa and will be happening more,” said Elmore.
“It’s pretty dire particularly for our later planted corn. It looks terrible, like onion fields it’s rolled up so tight,” Wiebold said of fields in Missouri. “You can’t find water in the ground. I’ve never seen it like this before.”
Wiebold said triple-digit heat with prolonged drought gives corn farmers very little chance of success. Corn plants stop growing at about 95 degrees F and need about 86 F optimal temperature for pollination. Night-time temps need to be under 70 F for the plant to fill corn kernels after pollination, when pollen from corn tassels falls on the silks of each ear of corn.
High night-time temperatures have hurt U.S. corn yields in the last two years. But that was not seen as the biggest threat to this year’s corn, crop specialists said.
“We’ve had days and days of bright sun, low humidity, high winds. That all adds up to rapid evaporation of water,” said Wiebold. “I don’t see any way around this from being a tragedy for our farmers.” (Reporting by Christine Stebbins. Editing by Peter Bohan and Dan Grebler)