"It should have a mass of roots the size of a basketball," he said as he shook the dirt off a yellowed stalk.

But after months with only a few drops of rain, the corn is weak and the roots have been gnawed away by worms. Even if the roots were stronger, there would not be anything for them to hold up -- most of the stalks do not have any ears.

Drought conditions have spread across the central United States and parts of the northwest. Much of the midwestern cornbelt has seen just half the average rainfall while parts of Illinois are now facing a severe drought after having received only a third of the average rainfall.

If US corn output drops substantially, global prices could jump. The United States produces 40 percent of the world's corn and exported 5.8 billion dollars worth in 2004. Japan, Mexico, Taiwan, South Korea and Egypt are the United States's largest customers.

It is too soon to tell how much of the nation's agricultural output will be affected, but the US Department of Agriculture has been steadily revising down its estimates.

And the forecast for Illinois -- which produces one sixth of the nation's corn -- shows little hope for reprieve.

"There's an incredible heat wave that's going to spread across (the midwest) this weekend," said Brad Rippey, a meteorologist with the USDA.

The timing couldn't be worse, he said, because "corn is at a critical stage of development."

Current industry estimates place this year's average yield at 130 to 140 bushels per acre. While that is substantially less than last year's record of 160.4 bushels per acre, it is not too far off from average yields.

"The general perception is that the western cornbelt is in average or above average conditions and it's offsetting to some extent the damage in Illinois," said William Tierney, a grains analyst with the USDA.

"Certainly Illinois is a very important state. It's number one or number two (in production) depending on the year. Clearly this has had an impact on the market."

A truer picture of the corn crop will come on August 12 when the USDA releases its first survey-based production estimate, Tierney said.

While corn prices have been choppy all summer at the Chicago Board of Trade, they remain relatively low, in part because of the leftover stocks from last year's bumper crop.

"At this point the probability of the corn crop being a major disaster seems to be at least countered by the fact that some of the crops north of the Mississippi seem to be pretty good," said Jerry Gidel, an analyst and broker with N.A. Risk Management Services in Chicago.

That is little comfort for Thanepohn, whose insurance agent has already written off most of his crop.

Most of Thanepohn's corn will get chopped up as fodder for his cows and he is now turning his hopes to his soybeans.

Unlike corn, which has a narrow period in which it can reproduce, soybeans flower for weeks. And while the crop has been under severe stress during the early parts of the growing season, some solid rain in the coming weeks would be enough to save the beans.

If the rains do not come, already strong soybean prices could push even higher. Global soybean stocks are tight because of two straight years of drought in Brazil.

It has been a tough summer for farmers like Thanepohn. First came news that a second case of mad cow disease had been discovered in the US. He saw the value of his cattle drop by 50 dollars a head. Then a dry spring led to an even hotter and drier summer.

Thanepohn, 53, and his son Phil, 28, farm 1,000 acres (400 hectares) and about 800 heads of cattle in a county about 50 miles (80 kilometers) west of Chicago. To supplement their income, Thanepohn also works as a crop insurance agent.

He has not had many calls from clients yet, but if the rains do not come soon he is going to get very busy, very fast.