Watch corn closely

When corn starts emerging from the ground, it pays to scout fields and find out what’s going on as the stand establishes. Timely scouting early in the season could be particularly helpful this year with a cool, wet spring.

“Get out into the fields, take stand counts and dig up some seedlings to see what’s going on with plant health,” urges Joel DeJong, an Iowa State University Extension field agronomist in northwest Iowa. “Also, how well did you do with planting depth and plant spacing? Keep an eye out for early-season insect pests, too.”

In April, rain across Iowa and cool soil temperatures kept farmers from planting corn as early as they wanted. Some corn did get planted the first half of April, but then the weather turned cold and it snowed in parts of northern Iowa.

Key Points

First step in evaluating corn emergence is a stand count.

Also, check to see if plants are evenly distributed.

Uniform growth is a key to maximize corn yield potential.


Corn planted in cool, wet soil will absorb water and begin to germinate. But growth of the corn seedling won’t begin until soil temperature gets above 50 degrees F at planting depth, he notes.

Seed that has absorbed water and sits in cold, wet soil waiting for the temperature to warm up is more susceptible to seed rot and seedling disease infections, insect feeding and death of the seed embryo.

Seed in cold, wet soil

This doesn’t necessarily mean fields that were planted early and then had rain and snow should be torn up and replanted. It means emergence will be more uneven than normal. It means stands will likely not be as high in population as expected.

Best bet is to finish planting the rest of your corn, says DeJong, and then see how the early-planted fields emerged and evaluate the population.

To maximize yield potential, it’s important to try to get a uniform stand, says Troy Griess, a Syngenta agronomist in northwest Iowa. “When you have some corn plants that are up and growing, and neighboring plants in the same row are struggling to emerge, you end up with plant-to-plant differences in height,” he notes. “And that’s not good.”

ISU research shows if larger neighboring plants with five leaves are next to smaller plants with three leaves, yield potential is reduced. That’s only a two-leaf difference, but the weaker plants compete like weeds with the larger, more dominant corn plants, reducing overall productivity.

If you dig around in the soil and find seed that didn’t germinate, the cause could be poor seed-to-soil contact, insects, fertilizer injury, chilling injury or seed decay. If seed germinated but didn’t emerge, the cause could be soil crusting, insects, fertilizer injury or seedling disease.

If you see gaps in corn stands or uneven plant height, look closely to determine the cause. It could be insects, sidewall compaction, improper planting depth, poor drainage, inconsistent fertilizer placement, poor seed quality or lack of cold tolerance in the seed genetics. If seed is missing, planter error such as skips could be the culprit.

What caused those gaps?

Once you find a probable cause for irregularities in a corn stand, you can make corrections in the future. “It may be too late to fix stand problems this year, but you’re more likely to find the reason for your problems by checking it out now than if you wait until harvest and just look at yield variability,” notes Griess.

First step to evaluate your new corn crop is to check the stand count. The accompanying table indicates the length of row equal to a thousandth of an acre for various row spacings. Take several counts throughout the field and calculate the average plant population. Compare the average stand count to your seeding rate to determine your stand establishment success.

The second step in evaluating corn emergence is to check stand uniformity. Are plants evenly distributed in the field or is the stand uneven? Does it have frequent gaps within rows? Getting plants to come up uniformly is a key step to maximize yield potential. Research indicates a potential yield loss of up to 8% when there is a 10-day delay in emergence between corn plants within the same row.

Variations in soil temperature and moisture probably create most cases of uneven timing of germination and uneven corn emergence, says Griess. Also, planting before soil conditions are favorable can cause sidewall compaction from disk openers, leading to uneven emergence.

Keep in mind, for corn to emerge it needs an accumulation of 100 to 110 growing degree units from the date of planting. With warm soil conditions, corn can emerge in a week, but with cooler temperatures emergence can take three weeks or more. The longer it takes for emergence, the more opportunity for insects and diseases to affect the stand.

ISU Extension has a new website to help monitor pest problems at www.ncipmpipe.org.

Know your seed treatment

Even if you planted seed that was treated with an insecticide and a fungicide, you still should scout fields and keep an eye out for insect and disease problems on corn seedlings.

Much depends on which product the seed was treated with and at what rate, says Troy Griess, an Iowa-based agronomist with Syngenta. You should become familiar with the seed treatment used so you’ll know which pests might not be affected and might be most likely to show up.


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PEST WATCH:
“Weather plays a critical role in determining insect pressure,” says Syngenta agronomist Troy Griess (kneeling). At a scouting session on a northwest Iowa farm, he explains which pests to watch for in corn.

This article published in the May, 2011 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.