The bulk of Indiana's corn crop — and much of the Corn Belt's crop — is moving beyond the pollination period and into the early stages of the important grain-filling period. Success during the next 45 to 60 days will be measured in terms of kernel set and kernel weight, says Bob Nielsen.

The Purdue University corn specialist says the degree to which the grain-filling period is successful depends primarily on whether the solar-powered photosynthetic factory growers have worked so diligently to construct back in May and June will operate efficiently through early September.

"The earliness of planting for many growers, coupled with lengthy periods of above-normal temperatures this year, set the stage for an early maturity date for quite a bit of the Indiana crop," Nielsen says. "The silking progress to date has been on par with the record-setting earliness of 2004 and certainly reinforces the likelihood for an early maturity to this crop and prospects for more rapid grain drydown in the field prior to harvest than last year's nightmare."

But Nielsen says there are several key factors that could make or break the yield potential of this year's crop.

1. "It's no secret that there yet exist quite a few ugly fields of corn that remain stunted and uneven in their development," Nielsen says. "The primary culprit was the excessive damage to the root systems from lengthy periods of saturated soils in May and June. Most of these fields will not come close to achieving their maximum yield potential."

2. The frequent and excessive rains of May and June occurred during the establishment of the root systems of corn plants. In addition to outright root death, Nielsen says the consequences of extended periods of wet soils include the development of a shallow root system.

"If the rain spigot would shut off for the remainder of the grain-fill period, drought-like symptoms would quickly develop and take its toll on kernel survival and kernel weight," he says.

3. Conditions have been favorable for early infection of certain important foliar diseases of corn, including gray leaf spot. Significant loss of photosynthetically active leaf area due to such diseases, or drought, or nitrogen deficiency, or hail damage during the grain filling period would weaken stalk integrity and increase the plants' susceptibility to root and stalk rot organisms, Nielsen adds.

"This can occur when photosynthetically challenged plants respond by cannibalizing or remobilizing stored carbohydrate reserves from the lower stalks and leaves to the developing grain on the ears," he says. "Fewer carbohydrates are available for maintenance of root health and the removal of carbohydrates results in physically weakened lower stalks. Grain yield suffers and harvestability can be compromised."

4. Above-normal temperatures during the grain-filling period are not favorable for optimum yield, Nielsen says. Excessively warm temperatures encourage a faster grain-filling rate per day — which is good — but a shorter grain-filling time period — which is not good.

"The abbreviated length of the grain-filling period during warm temperature periods tends to outweigh the benefits of faster daily grain fill rates," Nielsen says.

Nielsen says on the positive side, if soil moisture remains adequate, plants remain healthy and temperatures moderate soon, there is tremendous yield potential.