Take Time To Check Your Corn Stand

Take Time To Check Your Corn Stand

ISU Extension agronomists are getting questions about soybean planting, corn replanting, and weed control from farmers.

Why is my corn coming up so slowly? That was an often-asked question earlier this month in many areas of Iowa. Now that the calendar has progressed into the last week of May, farmers are asking—is there much replanting of corn going on in Iowa?

WALK YOUR FIELDS: Wet soil conditions at time of ammonia application may result in sidewall compaction from the ammonia knife, leaving a vertical gap for free ammonia to collect. If the corn seed, young roots or seedling plants come into contact with free ammonia, plant injury may occur.

Mark Johnson, an Iowa State University Extension field agronomist in central Iowa, has this observation: "Much of the corn planted this spring went into cold soils, or the soils became cold shortly after planting, so you should keep an eye on the crop for signs of injury as it emerges and gets established. If you have a disappointing stand, now is the time to determine whether replanting is necessary. Based on what I've seen so far, I don't think much replanting will be necessary, but you need to check the young corn as it emerges and gets established, and take stand counts to be sure of what you have."

Check soil conditions of planted fields—is there soil crusting?
As you check your newly established corn stand in each field, take note. Is the soil crusting?  Does it need a pass with a rotary hoe?

On newly emerged corn stands, says Johnson, here's what you need to check for:

1)  Population, seed depth and plant spacing. Did you get what you intended with your planter settings?

2)  Are there early-season weed issues? Is your pre-emergence herbicide program working?  Do you see any weed escapes? Be sure of the timing as to when to apply your post-emergence herbicide program. Plan ahead, and be ready to spray without delay.

3)  Watch for insects. Above ground insects to look for are black cutworm, armyworm, common stalk borer. Below ground insects could also be present. Do some digging around the plants and check for below ground insects. If you find gaps, missing plants or wilted plants—look for grubs, wireworms, seed corn maggot and Hop vine borer. The Hop vine borer bores up into the stem of the corn plant from below ground. Here is a corn insect scouting calendar to help organize your scouting activities.


Patience is required as corn develops slowly this spring
Working soil that is too wet can leave the field cloddy come planting time. Of course, you can get the crop planted in these conditions as planters have trash-whippers to move the clods to the side so your seeding depth isn't compromised, notes Johnson. But as soil dries out it shrinks and leaves opportunities for sunlight to reach below the soil surface. This will trigger the coleoptile of the corn plant to open underground. Next thing that happens is this corn will not emerge and instead it will leaf out underground. Check your stand and be sure to dig some seedlings and check the roots.

Watch for signs of ammonia burn on corn seedlings, he cautions. Wet soil conditions at time of ammonia application may result in sidewall compaction from the anhydrous ammonia application knife, leaving a vertical gap for free ammonia to collect. If the corn seed, young roots or seedling plants come into contact with free ammonia, plant injury may occur. That can slow down corn plant growth and, in severe cases, kill the plant.

When does soybean seed need inoculant?
Another question asked by farmers this past week— Does soybean seed need an inoculant when you plant into fields that have been corn-on-corn for several years?

"That's a great question, with widely varying opinions," says Clarke McGrath, Iowa State University Extension field agronomist at Harlan in western Iowa. "We don't have a lot of recent ISU data on inoculants, and inoculants have come a long way in recent years in terms of product improvement. Newer, novel strains of rhizobium are being offered, and most can be applied at the seed dealership; they are easier to use than the products in the past, and are more durable and typically don't cost a lot. Most of the inoculant products farmers are using are in the $2 to $5 per unit range."


Should you apply inoculant on beans in corn-bean rotation?
Do you need inoculants on beans in a corn-bean rotation where beans are planted in the field every other year? "We used to say an inoculant wasn't necessary in this situation," says McGrath. "But I'm seeing data from recent years that show positive returns on the use of the newer inoculant products. Granted this isn't ISU data, so rather than give a blanket endorsement, I'd say give them a shot in some strip trials on your farm if you haven't tried them recently. Also talk with your local seed dealer and other seed dealers and see how the products the dealers are familiar with are performing in your area."

What's the answer to the question about fields which haven't been planted to beans for three or more years? "In these situations I recommend using an inoculant," says McGrath. "Current land-grant university recommendations for states in the Upper Midwest concur: you should use an inoculant if fields have no history of soybean production in the past three to five years; or if soil pH is below 6.0, or if you have sandy soil, or low organic matter, or if the field has been flooded for more than a week."

Keep an eye out for Palmer amaranth in your fields
Farmers are also asking questions about a new weed they've been hearing about in the news. Palmer amaranth is a tough to control weed, a new weed in the Upper Midwest that's moved up from southern states into Iowa and other northern Corn Belt areas in recent years. One way to control it emphasizes the need for timely application of foliar-applied postemergence herbicides, notes McGrath.


Weed scientists point out those foliar-applied herbicides must be applied before Palmer amaranth plants are taller than 4 inches. Most crop consultants, agronomists and other weed management specialists are very familiar with the growth rates of waterhemp and many other weed species. But perhaps they are less familiar with the growth rate of Palmer amaranth—since it's a new weed in the Upper Midwest. The University of Illinois has put together a video, using time-lapse photography demonstrating the relative growth rate differences between waterhemp and Palmer amaranth.

During the filming in a greenhouse, both weed species emerged on the same day, and the plants were photographed every other day for a month. The photos show that Palmer amaranth plants reached a 4 inch height in less than 10 days after emergence. The bottom line is, timely applications of foliar-applied herbicides require vigilant scouting throughout a large part of the growing season.

Click on this link and watch waterhemp vs. Palmer growth rates
"This is a must-see online video," says McGrath. "I spent significant time during winter meetings discussing waterhemp and palmer amaranth management with growers and agronomists. I wish I would have had this set of pictures to illustrate exactly why we need to stay on top of weeds in fields, especially those two weeds. The video illustrates this much better than words!"

He adds, "The words I leave with you regarding this weed are: use a full labeled rate of residual herbicide; scout often; spray postemergence herbicides early; scout often and hit them again if needed. After seeing these pictures you'll know why I say this."

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