Illinois corn producers are learning at the combine what a summer of erratic weather cost them, with the state's weakest yields concentrated in areas hit by warm overnight temperatures during pollination and excessive rainfall.

Lance Tarochione, a DeKalb/Asgrow agronomist who covers western Illinois, says growers are discovering the results of less-than-ideal growing conditions as harvest rolls on. His field assessments point to two main drivers behind the yield shortfalls.

The first is heat that arrived at the wrong time. Warm overnight temperatures during the pollination window stressed the crop during its most yield-sensitive stage, limiting kernel set in affected areas.

The second is water — too much of it. In parts of his territory, saturated soils through the summer added further pressure on root systems and final yields.

Where is the damage worst?

Tarochione is blunt about the geography of the losses. "The worst corn in the state by far are the…" he said, pointing to the regions that absorbed the heaviest rainfall and the warmest nights during critical growth stages.

His observations add agronomic detail to what Illinois growers are seeing in the yield monitor this fall: a crop that entered the season with strong potential but lost ground to a weather pattern that swung from one extreme to another.

What should growers take from it?

For producers weighing hybrid selection, planting decisions and input spending for next season, the takeaway from this harvest is that stress timing mattered as much as stress type. Fields that escaped warm nights during pollination — or dodged the heaviest rains — are performing noticeably better than those that caught both.

Tarochione's continued harvest-season field reports should offer a clearer picture of how widely the damage extends across western Illinois and how much variance growers will see field to field.