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Take time to walk fields

Most of us will remember the spring of 2012 — at least if our memory bank accurately safeguards the data. We were all surprised and probably pleased by one of the warmest months of March in history, and now as April rushes by, conditions are holding closer to normal. By the time you read this, who knows what the year will offer.

To no one’s surprise, some corn was planted in Iowa starting as early as the third week in March! It’s the first year I remember that we all watched and anxiously awaited (and yes, some ignored) the crop insurance date. This year’s was April 11 for corn. A colleague recently reminded us of the old saying, “The early bird gets the worm.” A friend promptly revised it a bit by adding, “... or gets the burn!” Certainly early planting opens us up for more chance of frost damage as the crop progresses through its early stages of development.

Evaluate your stand

The month of May is a great time for you to evaluate corn stands. What looks good? What doesn’t? Why? What action should be taken? Two situations may especially cause you to consider replanting:

Corn emerged non-uniformly resulting in different plant developmental stages within a row. Replanting a field like this will not likely benefit anyone as long as plant populations are reasonable. 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%. Estimate yield loss in fields exhibiting non-uniform development using a tool on uneven emergence posted at our website listed below.

Corn populations are significantly lower than desired. Replanting may benefit you in this case. Consider several things and make comparisons when determining if a specific field fits this category:

Estimate stands. Measure the existing plant population in several random areas in the field. Use the “Replant checklist” (found at www.agronext.iastate.edu/
corn/production/management/planting/replanting.html
) 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.

The table below 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.

For example, you have a field that may need replanting, and you can replant by May 18. You originally planted on April 26, and the field has only 24,000 emerged plants per acre. Is there a yield advantage to replanting? The yield potential associated with leaving the existing stand is 95% — since the original planting date was between April 20 and May 5 and the population is close to 25,000 plants per acre.

If the field is replanted on May 18 to achieve 35,000 plants per acre, yield potential is about 87%. In this example, the producer will likely realize greater yield potential by leaving the original stand and not replanting. Also, extra costs are associated with replanting not only upfront with the actual replant costs, but also after harvest due to higher grain moisture content.

The decision regarding replanting is rarely an easy decision. Numerous factors determine a field’s yield potential. Consider data like that presented in the table as a tool to use in approximating what may result — based on our best available research data. Please realize, though, that actual yield losses may be greater or less than what is shown.

Elmore is the Iowa State University Extension corn agronomist.

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This article published in the May, 2012 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.