One veteran farmer who primarily irrigates but also has some dryland on soils underlain with gravel has already proclaimed this his worst crop since he's been farming. The corners where the irrigation don't reach, for example, are drying up. He doesn't expect corn there to make an ear at this point.

What's striking is that in 2007, another very dry year in that area, the non-irrigated corn made 80 bushels per acre. The difference this time was that the drought and heat came much earlier, and the corn was planted later.

Bob Nielsen, Purdue University corn specialist, agrees that there are many fields in the state that have been or are still under stress. From his observations, some of the worst corn he's seen is in northeast Indiana. Most of it was planted late. Some of it reached pollination during the center of the hot, dry stretch.

"Corn won't be wet at harvest like it was in 2009," he says. "That year we ran behind all year on growing degree days. This crop started out three weeks late but is now only a week behind because of the heat."

That's the good news.' The bad news is that the heat and dry conditions are leading to pollination problems. It can be anything from the pollen shedding before silks elongate, to tip die-back as the plant recognizes it's under stress, and aborts kernels.

One similarity to last year is the high nighttime temperatures during this heat wave. Corn doesn't stop respiring normally when it stays hot at night. Instead of using the sugars made during the day to put starch into the ear, a higher than usual percentage is used up to keep the plant going. Nielsen says that factor may be one of the things that trigger kernel abortion.

It also typically results in less than an optimum amount of starch in the kernels. Last year many believe it was one reason why the USDA August estimate was more than 10 bushels higher than the final estimate in January for the 2010 crop, nearly a record difference form the first estimate to the last.

Speaking of which, the USDA first estimate of the 2011 crop, the August estimate, is due out tomorrow. Nielsen agrees that it will be interesting to see where USDA pegs corn yields, especially in Indiana. Stay tuned!