Progress of corn planting and corn emergence

Two questions about corn
1. Is the corn planting window closing?
2. What about corn that is already planted?

As of Sunday, USDA-NASS reported half of Iowa’s corn lay in seed beds, the other half in seed bags. That rate puts us 18 percent ahead of the five-year average. Forty-one percent of our anticipated crop was planted in one week, with only 4.3 days suitable for fieldwork. If we can use that number for days corn was planted, that’s 5.9 million acres in 4.3 days or 1.37 million acres per day. Proving we can plant a lot of corn quickly in Iowa when conditions are right. Unfortunately, forecast conditions this week aren’t too favorable right now. How should we think about this? 

click image to zoom Corn already planted

By April 22 we had nine percent of Iowa’s corn planted. Four percent of that was planted between April 16-22, four percent between April 9 – 15, and 1 percent prior to April 8.  Depending on your specific location, all of the corn planted prior to April 15 should be emerged or very close to emerging now based on average heat unit accumulations across the state.  However, heat unit accumulation (growing degree days or GDD) has been a bit less in the northern third of the state, so corn in those areas planted before April 15 may be close to emergence but not quite there yet. It takes about 90-120 GDD’s from planting to emergence.

Corn planted after the April 15, including that planted last week, should be well along in the germination process but not yet emerged. For more information on this, read the article Elwynn Taylor and I wrote about corn’s germination process.

R. ElmoreFigure 1. Corn planted April 4 emerged April 23, right on schedule with about 124 GDD accumulated from planting. Once emergence occurs, evaluate plant stands carefully – whether you expect good emergence and seedling survival or not. Poor stands and plant-to-plant variability lower yield potential. However, depending on the potential date of replant, keeping the surviving stand may be the best option – even with variable plant heights and development.

There are two situations that may cause you to consider replanting: 

1. If corn plants emerged non-uniformly, resulting in different plant developmental stages within a row but plant populations are reasonable, replanting will not likely be of benefit. Although the smaller plants compete with their larger neighbors for resources, only extreme conditions warrant replanting. If half the plants are two-leaves behind the rest of the plants within a row, yields can be reduced by 5 to 10 percent. You can estimate yield loss in fields exhibiting non-uniform development by using a tool on uneven emergence posted at our website.  
2. If corn populations are significantly lower than desired, replanting may be of benefit. Consider several things and make comparisons when determining if a specific field fits this category:

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  • Estimate stands. Measure the existing plant population in several random areas in the field. Use the ‘Replant Checklist’ for steps to evaluate an existing stand in a problem field.
  • Estimate yields. The most important factor in deciding whether or not to replant is to calculate expected yield with the current stand versus what you could potentially have if you replanted. Table 1 provides guidelines for this decision. The data shows relative yield potential for numerous planting dates and plant populations based on recent yield data, planting date trends and modern ranges in plant populations.