Unusually warm, dry weather in the past month has led some central Illinois growers to get a jump on fieldwork. While there is nothing wrong with getting fields in shape early, University of Illinois crop sciences professor Emerson Nafziger says that planting well ahead of normal is unlikely to result in higher yields.

“We know that some corn and possibly some soybeans were planted as early as February this year,” Nafziger says. “While there were reports in 2016 of higher yields from early- compared to late-planted crops, ‘the earlier the better’ typically doesn’t work well when it comes to planting corn or soybeans. Yields are usually no higher for crops planted in March or early April compared to those planted in late April or early May, so there’s little reward for taking the risk of very early planting.”

The primary cause of stand loss in both crops is heavy rainfall soon after planting; Nafziger says stand problems due to wet soils are as common with May planting as with April planting. The danger of frost damage, which was once a major reason to delay planting, is not as significant for either crop these days, but it is higher with very early planting.

Planting very early also affects insurability and, if the crop needs to be replanted, can increase production costs. For corn, the earliest insurable dates for planting are April 10, April 5, and April 1 for northern, central, and southern Illinois, and for soybean they are April 24, April 20, and April 15.

Nafziger’s recent research shows that, on a percentage basis, yield penalties from delayed planting are almost identical for corn and soybean. That is a departure from earlier findings that showed corn yield declined faster than soybean yields as a result of planting delays through May.

“Our long-held idea of planting corn first and then starting to plant soybean requires rethinking and possible adjustment,” Nafziger says. “One approach is that those with more than one planter might start planting both crops at the same time rather than finishing corn first. If planting is delayed past mid-May, though, then planting corn becomes a higher priority because corn yield declines more quickly than soybean yield when planting is very late. Of course, we hope that we can get both crops planted by early May so they can get off to a good start.”