"On some cold, wet spring days like today, you wonder whether the (corn) seed is better off in the bag or in the field,” says Emerson Nafziger, University of Illinois Agronomist.

Wet soils and cold weather have disrupted planting across large parts of the Upper Midwest and all of Iowa.

“If the whole (corn) crop got planted May 10 instead of May 1, we would not see a big drop in yield,” Nafziger says. “We don’t start losing a lot of yield until after mid-May, and even then losses accumulate at a modest rate. “We may have forgotten, but there is some advantage for the corn seed to be in a fairly warm soil, ready to germinate and emerge in five to six days.

“Last year, most of the (Illinois) corn was planted after May 1, and we still had good yields. So we know that what happens during the season is more important than when the crop gets planted.

Minnesota data bears this out. University of Minnesota planting date studies show highest corn yield typically occurs when planting is completed by mid-May. "Corn emergence date is not likely to differ greatly between April 21 and May 5 planting dates this year given the limited growing degree days that have accumulated since April 21 and are expected over the next few days," a data summary shows. "This will likely result in similar grain yields between these planting dates, assuming that stand establishment with the early planting date is adequate."

“Think of corn planting in thermal time (growing degree days) instead of calendar time,” Nafziger advises. Growth is slow when soils are cool anyway, so planting delays early in the season don’t mean big delays in development.

No plants left behind

 “No plants left behind” is Fred Below’s motto for planting seasons like this. “Waiting for reasonable conditions is more important than early planting in cold, wet soils like we have (in central Illinois),” says the University of Illinois corn physiologist. “Get every plant up near the same time and off to a good start. You never make up for lost yield due to uneven emergence.

 “Last year, we did not plant here (central Illinois) until mid-May, and the yields were considerably better than we thought they’d be. Once planted, the crop emerged uniformly in five or six days.

“Seed treatments surely help to protect the seed, but they don’t warm the soil.”