With 96 percent of the corn crop planted and 78 percent emerged by mid-May, there should be a lot of joy about the 2010 Illinois corn crop. Instead, many farmers are discussing the need to replant and other woes. Most have observed that the crop is not growing well, and that it has poor color.

So, is the crop off to the great start discussed several weeks ago or not?

Emerson Nafziger, U of I Extension agronomist, said, "The first point we need to remember is that the 'start' to the Illinois corn crop is not highly correlated with the 'end' -- final yield. The great starts in 2004 and 2005 ended with high and low yields respectively, and the poor starts in 2002 and 2009 ended with low and high yields respectively."

The growing season is long, and weather effects have a complicated interaction with how the corn crop is managed.

"While we can feel good about early planting and good stands at this point, trying to use current (May) crop condition to predict yield is simply a guess," Nafziger said. "We know that clear and visible negatives such as poor stands, uncorrected nutrient deficiency, or heavy weed competition will usually not result in high yields, but the effects of clear and visible positives at this point in the season are much less certain."

Nafziger said the corn crop in East-Central Illinois is developing as expected for the corn planted in late April, but the earlier-planted corn is slightly ahead of predictions due to the warmer temperatures in the first three weeks of April.

"With low temperatures in the 30s on May 8 and cool, cloudy, wet weather in most places since then, the crop still appears pale with slow growth," he said. "In fact, growth is usually fairly slow during early vegetative stages, and we tend to project weather that we don't like as also being poor for corn."

Whether or not cool weather in May affects final yield is a good question, but it's certain that weather patterns through the rest of the season have more effect on yield than temperatures during May, he added.

If corn is up with a good stand, water is not standing in the field, and all other management factors are in place, Nafziger reminds farmers that they have done all they can to set the crop up to reach its yield potential.

Once growth resumes with warmer temperatures and sunshine, the earliest-planted crop will quickly reach its rapid-growth stage when stem elongation begins. This happens at or just after the V6 growth stage, and then accelerates, with most rapid stem elongation occurring after V9 or V10 when the internodes in the central part of the stalk start to elongate. After V6, rapid leaf appearance and expansion add quickly to leaf area, and this in turn increases the photosynthetic capacity, which further increases the rate of growth.

"With luck, the crop will look better and be growing rapidly by early June in most fields," he said. "If the weather into June is good, then we'll forget the slow growth we're seeing now and start to look forward to having a good crop canopy in place and a good start to pollination by early July."

For more information on the latest crop news, check out The Bulletin, an online publication written by U of I Extension specialists in crop science.

SOURCE: University of Illinois.