The variability in daily accumulation of GGDs during April means that emergence can take anywhere from one to three weeks. Having corn take 20 days or more to emerge is not necessarily a problem if both emergence percentage and emergence uniformity – the time between first and last emergence within a field – are good. Under cool temperatures, it is normal for emergence to be spread over four or five days in a field.

People often worry that non-uniformity of emergence will reduce yield. Plants that lag in their development tend to stay behind and often lose the competition for light, water and nutrients. Although it is not true that such plants end up as “weeds” – that they reduce the yields of remaining plants – the larger plants do not make up for the yield lost from the plants that get left behind.

Non-uniform emergence is a problem if it is related to factors such as seedling damage, soil crusting, or low seed vigor. However, uniformity is also affected by temperature (GDD accumulation rates), as is the time between planting and emergence.

“I suggest that we consider emergence to be ‘uniform’ if it occurs over the time it takes to accumulate 20 or 25 GDD, whether that is one day or five days,” Nafziger says. “As with other aspects of corn development, basing events on ‘thermal time,’ or GDDs, works better than using time measured in hours or days. The practical effect is that, once it warms up, plants that emerged in 110 GDD and those that took 130 GDD to emerge will differ very little in their stage of development. Once we get to June, 20 GDD is only one day’s accumulation.”

Although it takes patience to wait until wet soils dry out before planting, remember that it is still early, and yield potential is not yet at risk from delayed planting.

“While planting date responses vary among years and sites in our research, we can consider the planting date response to be flat for the month of April, with losses starting to pick up slowly in early May,” Nafziger said. He cautioned that the damage related to working or planting into soils that are too wet can more than offset the gains related to early planting.

“While we hope to get much of our crop planted by the end of April, what happens after planting remains a lot more important to the corn crop than the exact date we are able to plant,” he says. “We need look back only one year to see that early planting does not guarantee high yields.”


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