When early August rolls around, the professional farm managers at Soy Capital Ag Services head for the fields to do their annual pre-harvest physical exam on the corn acres they oversee.

It helps them make key profit-enhancing decisions, particularly on harvest timing and hybrid selection.

Producers across the Corn Belt may want to do something similar.

“We check our managed fields all season long, starting at emergence, to monitor each hybrid's individual performance,” says Dave Klein, Soy Capital, Bloomington, IL. “But the pre-harvest check is especially important because of all it tells us.”

One priority is to estimate yield. “We recognize that these are only estimates,” says Klein. “Nevertheless, they indicate whether the yield will be above or below government and private forecasts. If yields look to be above the early forecasts, we can increase our forward pricing before the larger crop becomes general knowledge and prices drop.”

Ideally, they make the yield checks just prior to dent — generally around the first or second week of August in central Illinois. “The closer to harvest, the more accurate the estimates,” Klein notes.

The Soy Capital managers use the University of Illinois formula for estimating yields, although they modify it slightly based on their experience with the formula and on local growing conditions. (See sidebar on page 18.)

“For example, we have adjusted it in some years, and with some hybrids, to reflect the possibility of lower or higher test weight,” Klein says. “That's because we've learned that late July or early August rainfall amounts can affect test weight enough to add or subtract 5-10 bu/acre from the formula estimate.”

Another priority for the farm managers in the pre-harvest exams is to detect diseases or insect damage that can weaken plants and create the need for early harvest.

In 2000, for example, common rust was prevalent. “It affects individual hybrids differently. A strong windstorm, coupled with intense rainfall in early August really pressured some hybrids, leading to anthracnose and diplodia stalk rot,” Klein notes. “You couldn't see the extent of damage from the road. We spent several days in rain slickers and boots examining the fields.

“We followed that with an aerial survey so we could see the full extent of damage. During those fly-overs, we took photos of the damage so we could show the landowners and farm operators the need for early harvest. We alerted our operators that an early harvest would be critical for salvaging yield on affected hybrids.”

In 2001, the pre-harvest check uncovered a surprising amount of European corn borer damage. That also called for early harvest of some hybrids to save yields.

“As a result of finding those large corn borer numbers last year, we increased our Bt corn from 14% (in 2001) to 33% for this year,” Klein notes. “We also observed some conventional hybrids that showed good natural tolerance to corn borers and we increased those.”

Early harvests generally have meant greater drying costs, but the higher yields have easily offset that expense when problems existed, Klein points out.

Although the pre-harvest checks provide a good idea of the relative yield of various hybrids, Soy Capital does not make final hybrid decisions until after harvest. “We combine our pre-harvest observations with actual yield results,” says Klein. “Actual yield is still the key, but our pre-harvest observations often help explain why a particular hybrid may not have performed up to expectations, especially in a given field.”

Klein says the insights the managers get from the pre-harvest observations are particularly important in these days of rapid hybrid turnover. “Many hybrids are released before seed companies know their optimal management,” he says. “By our observing new numbers early in different environments at different populations and with different cultural practices, we can more quickly identify their best uses in the following years.”

Estimating Yields

Farmers who want to estimate corn yields can find the University of Illinois (U of I) formula in the Web-based version of the Illinois Agronomy Handbook at: http://web.aces.uiuc.edu/aim/IAH/ch2/ecy.html.

It's a very simple concept, says U of I agronomist Emerson Nafziger. But inaccuracies can come from using non-representative samples. “People tend to be optimistic and often gravitate to better parts of the field for sampling if they don't like what they see,” Nafziger notes.

Inaccuracies also can come from final kernel size being different from that assumed in the formula. However, the formula allows the user to adjust for this if conditions warrant it.