The Illinois corn crop condition continues to deteriorate, with less than 40 percent now rated as good to excellent on June 24, according to University of Illinois crop sciences professor Emerson Nafziger
On the positive side, the current corn crop has good color, is mostly disease-free, and has uniform stands with few drowned-out areas. These factors will contribute to increasing kernel set in fields pollinating now, at least where there is enough soil water. Cooler weather this past week has prolonged the period of adequate water, and cooler nights reduce respiration, thus helping the sugar supply.
On the negative side is the lack of rainfall, with deficits for May and June ranging from 1 to 6 inches in different parts of Illinois. On June 26 the U.S. Drought Monitor showed the entire state as dry, with most of the state in moderate to severe drought and the southern counties in "extreme drought."
As the crop enters the critical yield-producing stage, many are wondering about the effects the lack of soil water has had, and will have, over the next weeks. "The 2012 corn crop is well-rooted, healthy, and tough, but it's unrealistic to expect it to continue to thrive as the soil water supply continues to decline in dry areas," Nafziger said. Plants that are unable to take up enough water to keep leaves from rolling in the afternoon are not fully productive, and this takes a toll on the crop.
"As of June 24, 17 percent of the state's corn crop was pollinating, the highest percentage for this date on record," he continued. "This week we would expect most of the crop that was planted by mid-April in central and southern Illinois to begin to pollinate, bringing the number by July 1 to perhaps 40 percent."
While pollination is the most critical period in terms of yield potential, breeding for aggressive emergence of ear shoots and silks has considerably lessened the likelihood that pollination will fail completely. However, the number of kernels set may be lowered on plants that have been undergoing stress from dry soils, and the number of fertilized kernels that survive the weeks after pollination may continue to decline if the weather stays dry.
Observers in the fields note that corn is entering or approaching pollination while plants are shorter than normal. This raises questions about the connection between plant height and yield.
"Plant height is the best visible indicator of how well the plant has been able to take up the water it needs to expand cells," Nafiziger explained. "Cell expansion is sensitive to water supply, so shortened internodes are one of the first things we notice on plants that have struggled to take up enough water to keep growing."